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 *
from collections import *
from bisect import *
    
t = int(input())

def solve():
    n = int(input())
    arr = [int(x) for x in input().split()]
    m = max(arr)
    flag = False
    for i in range(n):
        if arr[i] == m and ((i+1 < n and arr[i] > arr[i+1]) or (i-1 >= 0 and arr[i]> arr[i-1])):
            flag = True
            print(i+1)
            break
    if not flag:
        print(-1)


p = 1
while t:
    t-= 1
    ans = solve()
    # print('Case #'+ str(p)+': '+str(ans))
    p+=1 