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

t = int(input())
for i in range(t):
    n = int(input())
    piranjas = [int(fish_size) for fish_size in input().split()]
    max_size = max(piranjas)
    ans = -1
    for i in range(n - 1):
        if piranjas[i] == max_size:
            if piranjas[i + 1] < max_size:
                ans = i + 1
                break
    if ans != -1:
        print(ans)
        continue
    for i in range(n - 1):
        if piranjas[i + 1] == max_size:
            if piranjas[i] < max_size:
                ans = i + 2
                break
    print(ans)