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 cal(n, arr):
    if n == 1:
        return -1
    dic = {arr[0]:True}
    maxi = 0
    for i in range(1, n):
        dic[arr[i]] = True

        if i == n-1 and arr[i] > arr[i-1] and arr[i] >= arr[maxi]:
            maxi = i

        elif i != n-1 and (arr[i] > arr[i-1] or arr[i] > arr[i+1]) and arr[i] >= arr[maxi]:
            maxi = i

    if len(dic) == 1:
        return -1
    return maxi+1


t = int(input())
for _ in range(t):
    n = int(input())
    arr = list(map(int, input().split()))
    print(cal(n, arr))
