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 solve():
    # put code here
    n=int(input())
    arr=[int(v) for v in input().split()]
    mx=max(arr)
    for i in range(n):
        if (arr[i]==mx and (
            i>0 and arr[i-1]<arr[i] or
            i<n-1 and arr[i+1]<arr[i]
        )):
            print(i+1)
            return
    print(-1)


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