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 i in range(int(input())):
    n = int(input())
    a = [int(i) for i in input().split()]
    if len(set(a)) == 1:
        print(-1)
    else:
        if a.count(max(a)) == 1:
            print(a.index(max(a)) + 1)
        else:
            for j in range(a.index(max(a)), n - 1):
                if j == 0:
                    if a[j] > a[j + 1] and a[j] == max(a):
                        print(j + 1)
                        break
                else:
                    if (a[j] > a[j + 1] or a[j] > a[j - 1]) and a[j] == max(a):
                        print(j + 1)
                        break