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

#   ==========     //\\       //||     ||====//||
#       ||        //  \\        ||     ||   // ||
#       ||       //====\\       ||     ||  //  ||
#       ||      //      \\      ||     || //   ||
#   ========== //        \\  ========  ||//====|| 
#  code


def solve():
    n = int(input())
    a = list(map(int, input().split()))

    if a == [a[0]] * n:
        print(-1)
    else:
        k = max(a)
        for i in range(n):
            if a[i] == k:
                if i + 1 < n:
                    if a[i] > a[i + 1]:
                        print(i + 1)
                        return
                if i - 1 >= 0:
                    if a[i] > a[i - 1]:
                        print(i + 1)
                        return
        print(-1)

def main():
    t = 1
    t = int(input())
    for _ in range(t):
        solve()

if __name__ == "__main__":
    main()