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

for _ in range(int(input())):
    n = int(input())
    *fish, = map(int, input().split())
    mn = min(fish)
    mx = max(fish)
    if mn == mx:
        print(-1)
    else:
        for i in range(n):
            if i > 0 and fish[i] == mx and fish[i - 1] < mx:
                print(i + 1)
                break
            if i < n - 1 and fish[i] == mx and fish[i + 1] < mx:
                print(i + 1)
                break
