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 helper(arr):
    m = max(arr)
    for i in range(len(arr)):
        if arr[i] == m:
            if i == 0 and arr[i+1] < m:
                return i+1
            elif i == len(arr)-1 and arr[i-1] < m:
                return i+1
            elif 0 < i < len(arr)-1 and arr[i-1] < m:
                return i+1
            elif 0 < i < len(arr)-1 and arr[i+1] < m:
                return i+1
    return -1

for _ in range(int(input())):
    n = int(input())
    a = list(map(int, input().split()))
    
    if a.count(a[0]) == n:
        print(-1)
    else:
        ans = helper(a)
        print(ans)