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())
    array = list(map(int, input().split()))

    max_val = max(array)
    exists = -1
    for i in range(n):
        if array[i] == max_val:
            if i == 0:
                if array[i] > array[i + 1]:
                    exists = i
                    break
            elif i == n - 1:
                if array[i] > array[i - 1]:
                    exists = n - 1
                    break
            else:
                if array[i] > array[i + 1] or array[i] > array[i - 1]:
                    exists = i
                    break
    
    if exists == -1:
        print(exists)
    else:
        print(exists + 1)