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())
    arr = list(map(int, input().split()))
    if [arr[0]] * n == arr:
        print(-1)
    else:
        max_val = max(arr)
        for i in range(n):
            if i == 0:
                if arr[0] == max_val and arr[1] < max_val:
                    print(1)
                    break
            elif i == n - 1:
                if arr[n - 1] == max_val and arr[n - 2] < max_val:
                    print(n)
                    break
            else:
                if arr[i] == max_val and (arr[i - 1] < max_val or arr[i + 1] < max_val):
                    print(i + 1)
                    break