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())

while t:
    n = int(input())
    ans = -1
    ar = list(map(int, input().split()))
    max = ar[0]
    for i in range(1,n):
        if (ar[i] != ar[i - 1]):
            if (ar[i] >= ar[i - 1]):
                if (ar[i] >= max):
                    max = ar[i]
                    ans = i
            elif (ar[i - 1] >= max):
                max = ar[i - 1]
                ans = i - 1
    if ans != -1:
        print(ans + 1)
    else:
        print(-1)
    t -= 1