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 functools import reduce
import os
import sys
from collections import *
#from fractions import *
from math import *
from bisect import *
from heapq import *
from io import BytesIO, IOBase
input = lambda: sys.stdin.readline().rstrip("\r\n")
def value(): return tuple(map(int, input().split())) # multiple values
def arr(): return [int(i) for i in input().split()] # array input
def sarr(): return [int(i) for i in input()] #array from string
def starr(): return [str(x) for x in input().split()] #string array
def inn(): return int(input()) # integer input
def svalue(): return tuple(map(str, input().split())) #multiple string values
def parr(): return [(value()) for i in range(n)] # array of pairs
mo = 1000000007
inf=1e18
div=998244353
#print("Case #{}:".format(_+1),end=" ")
#print("Case #",z+1,":",sep="",end=" ")
# ----------------------------CODE------------------------------#
for _ in range(inn()):
    n=inn()
    a=arr()
    mx=max(a)
    ans=-1
    for i in range(n):
        if(a[i]==mx):
            if((i-1>=0 and a[i-1]<a[i]) or (i+1<n and a[i+1]<a[i])):
                ans=i+1
                break
    print(ans)

