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

def main():
    n = int(input())
    arr = list(map(int, input().split()))
    m = max(arr)
    for i in range(n):
        if arr[i] == m:
            if i > 0 and arr[i-1] < m:
                print(i+1)
                return
            elif i + 1 < n and arr[i+1] < m:
                print(i+1)
                return
    print(-1)
    




for _ in range(int(input())):
    main()