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 = [int(x) for x in input().split()]
    maxi = max(arr)
    max_ind = [i for i, val in enumerate(arr) if val == maxi]
    if len(max_ind) == n:
        print(-1)
        continue
    for i in max_ind:
        if i != n-1:
            if arr[i+1] < arr[i]:
                print(i)
                break
        if i != 0:
            if arr[i-1] < arr[i]:
                print(i)
                break
    else:
        print(-1)
                