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())
    l = list(map(int, input().split()))
    set_ = set(l)
    x = len(set_)
    if x == 1:
        print(-1)
    else:
        start = 0
        max_ = max(l)
        idx = (l.index(max_))
        r = False
        for i in range(idx+1, n):
            if l[i] == max_:
                start = i
            if l[i] < max_:
                r = True
                break
        if r and start!=0:
            print(start+1)
        else:
            print(idx+1)