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

t = int(input())
for i in range(t):
    n = int(input())
    a = [int(item) for item in input().split()]
    k = 0
    max = a[0]
    for i in range(n - 1):
        if a[i] < a[i + 1]:
            max = a[i + 1]
            k = i + 1
    if k == 0:
        if a[0] == a[-1]:
            print(-1)
        else:
            while a[k] == a[k+1]:
                k += 1
            print(k+1)
    else:
        for i in range(k, n-1):
            if a[i] > a[i+1]:
                print(i+1)
                break
