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())

def solve():
    n = int(input())
    arr = list(map(int, input().split()))
    if(len(set(arr)) == 1):
        print(-1)
    else:
        m = max(arr)
        for i in range(n):
            if(i == n - 1 and arr[i] == m):
                print(i + 1)
                break
            if(i < n - 1):
                if(arr[i + 1] != m and arr[i] == m):
                    print(i + 1)
                    break
            if(i > 0):
                if(arr[i - 1] != m and arr[i] == m):
                    print(i + 1)
                    break

for i in range(t):
    solve()