1
3
5 3 4
 6
5
5 3 4 4 5
3
1 1 1
5
4 4 3 4 4
5
5 5 4 3 2
3
1 1 2
5
5 4 3 5 5
 1
3
10 1 5

1
 1
-1
2
2
3
1
 1


from math import gcd
from bisect import bisect_left, bisect_right
from itertools import combinations
from itertools import permutations
from bisect import bisect_left
from math import ceil
from math import radians
from heapq import heapify, heappush, heappop, nsmallest
import bisect
from math import pi
from collections import deque
from math import factorial
from math import log, ceil
from collections import defaultdict
from math import *
from sys import stdin, stdout
import itertools
import os
import sys
import threading
from collections import deque, Counter, OrderedDict, defaultdict
from heapq import *
# from math import ceil, floor, log, sqrt, factorial, pow, pi, gcd
# from bisect import bisect_left,bisect_right
# from decimal import *,threading
from fractions import Fraction
mod = int(pow(10, 9)+7)
# mod = 998244353


def ii(): return int(input())


def si(): return str(input())


def mi(): return map(int, input().split())


def li1(): return list(mi())


def fii(): return int(stdin.readline())


def fsi(): return str(stdin.readline())


def fmi(): return map(int, stdin.readline().split())


def fli(): return list(fmi())


abd = {'a': 0, 'b': 1, 'c': 2, 'd': 3, 'e': 4, 'f': 5, 'g': 6, 'h': 7, 'i': 8, 'j': 9, 'k': 10, 'l': 11, 'm': 12,
       'n': 13, 'o': 14, 'p': 15, 'q': 16, 'r': 17, 's': 18, 't': 19, 'u': 20, 'v': 21, 'w': 22, 'x': 23, 'y': 24,
       'z': 25}


def getKey(item): return item[0]


def sort2(l): return sorted(l, key=getKey)


def d2(n, m, num): return [[num for x in range(m)] for y in range(n)]


def isPowerOfTwo(x): return (x and (not (x & (x - 1))))


def decimalToBinary(n): return bin(n).replace("0b", "")


def ntl(n): return [int(i) for i in str(n)]


def powerMod(x, y, p):
    res = 1
    x %= p
    while y > 0:
        if y & 1:
            res = (res * x) % p
        y = y >> 1
        x = (x * x) % p
    return res


graph = defaultdict(list)
visited = [0] * 1000000
col = [-1] * 1000000


def bfs(d, v):
    q = []
    q.append(v)
    visited[v] = 1
    while len(q) != 0:
        x = q[0]
        q.pop(0)
        for i in d[x]:
            if visited[i] != 1:
                visited[i] = 1
                q.append(i)
        print(x)


def make_graph(e):
    d = {}
    for i in range(e):
        x, y = mi()
        if x not in d:
            d[x] = [y]
        else:
            d[x].append(y)
        if y not in d:
            d[y] = [x]
        else:
            d[y].append(x)
    return d


def gr2(n):
    d = defaultdict(list)
    for i in range(n):
        x, y = mi()
        d[x].append(y)
    return d


def connected_components(graph):
    seen = set()

    def dfs(v):
        vs = set([v])
        component = []
        while vs:
            v = vs.pop()
            seen.add(v)
            vs |= set(graph[v]) - seen
            component.append(v)
        return component

    ans = []
    for v in graph:
        if v not in seen:
            d = dfs(v)
            ans.append(d)
    return ans


def primeFactors(n):
    s = set()
    while n % 2 == 0:
        s.add(2)
        n = n // 2
    for i in range(3, int(sqrt(n)) + 1, 2):
        while n % i == 0 and i % 2 == 1:
            s.add(i)
            n = n // i
    if n > 2 and n % 2 == 1:
        s.add(n)
    return s


def find_all(a_str, sub):
    start = 0
    while True:
        start = a_str.find(sub, start)
        if start == -1:
            return
        yield start
        start += len(sub)


def SieveOfEratosthenes(n, isPrime):
    isPrime[0] = isPrime[1] = False
    for i in range(2, n):
        isPrime[i] = True
    p = 2
    while (p * p <= n):
        if (isPrime[p] == True):
            i = p * p
            while (i <= n):
                isPrime[i] = False
                i += p
        p += 1
    return isPrime


def dijkstra(edges, f, t):
    g = defaultdict(list)
    for l, r, c in edges:
        g[l].append((c, r))

    q, seen, mins = [(0, f, ())], set(), {f: 0}
    while q:
        (cost, v1, path) = heappop(q)
        if v1 not in seen:
            seen.add(v1)
            path = (v1, path)
            if v1 == t:
                return (cost, path)

            for c, v2 in g.get(v1, ()):
                if v2 in seen:
                    continue
                prev = mins.get(v2, None)
                next = cost + c
                if prev is None or next < prev:
                    mins[v2] = next
                    heappush(q, (next, v2, path))
    return float("inf")


def binsearch(a, l, r, x):
    while l <= r:
        mid = l + (r-1)//2
        if a[mid]:
            return mid
        elif a[mid] > x:
            l = mid-1
        else:
            r = mid+1
    return -1


# def input():
#    return stdin.buffer.readline()


def readTree(n):
    adj = [set() for _ in range(n)]
    for _ in range(n-1):
        u, v = map(int, input().split())
        adj[u-1].add(v-1)
        adj[v-1].add(u-1)
    return adj


def treeOrderByDepth(n, adj, root=0):
    parent = [-2] + [-1]*(n-1)
    ordered = []
    q = deque()
    q.append(root)
    depth = [0] * n
    while q:
        c = q.popleft()
        ordered.append(c)
        for a in adj[c]:
            if parent[a] == -1:
                parent[a] = c
                depth[a] = depth[c] + 1
                q.append(a)
    return (ordered, parent, depth)


def isSubSequence(str1, str2):
    m = len(str1)
    n = len(str2)

    j = 0    # Index of str1
    i = 0    # Index of str2

    # Traverse both str1 and str2
    # Compare current character of str2 with
    # first unmatched character of str1
    # If matched, then move ahead in str1

    while j < m and i < n:
        if str1[j] == str2[i]:
            j = j+1
        i = i + 1

    # If all characters of str1 matched, then j is equal to m
    return j == m


def nextPowerOf2(n):
    count = 0

    # First n in the below
    # condition is for the
    # case where n is 0
    if (n and not(n & (n - 1))):
        return n

    while(n != 0):
        n >>= 1
        count += 1

    return 1 << count


def cou(n):
    c = 0
    while n > 1:
        c += 1
        n //= 2
    return c


def sortsec(l):
    return sorted(l, key=lambda x: x[1])


def BinarySearch(a, x):
    i = bisect_left(a, x)
    if i:
        return (i-1)
    else:
        return - 1


def subarray(A):
    r = set()

    p = {0}

    for x in A:
        p = {x | y for y in p} | {x}
        r |= p

    return len(r)


def setBitNumber(n):
    n |= n >> 1
    n |= n >> 2

    n |= n >> 4
    n |= n >> 8
    n |= n >> 16
    n = n + 1
    return (n >> 1)


def countSetBits(n):
    count = 0
    while (n):
        count += n & 1
        n >>= 1
    return count

def allsub(l):
    n = len(l)
    a=[]
    for i in range(n - 1):
        for j in range(i + 1, n):
            a.append(l[i:j])
    return a

for _ in range(ii()):
    n = ii()
    l = li1()
    if len(set(l)) == 1:
        print(-1)
        continue
    x = max(l)
    f=0
    for i in range(1,n-1):
        if l[i] == x and l[i - 1] < x:
            print(i + 1)
            f=1
            break
        elif l[i] == x and l[i + 1] < x:
            print(i + 1)
            f=1
            break
    if f==0 and l[0] == x and l[1] < x:
        print(1)
    elif f == 0 and l[n-1] == x and l[n-2] < x:
        print(n)
    elif f == 0:
        print(-1)