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 _ in range(t):
    n = int(input())
    b = list(map(int, input().split()))
    a = sorted(b, reverse=True)
    if sum(a) == len(a) * a[0]:
        print(-1)
    else:
        for i in range(n-1):
            if a[i] > a[i+1]:
                if b[-1] == a[i]:
                    for j in range(n - 1, -1, -1):
                        if a[i] == b[j] and b[j] > b[j - 1]:
                            print(j + 1)
                            break
                else:
                    for j in range(n-1):
                        if a[i] == b[j] and b[j] > b[j+1]:
                            print(j+1)
                            break
                break
