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())
    l = list(map(int, input().split()))
    if len(set(l)) == 1:
        print(-1)
        continue
    r = max(l)
    for j in range(n - 1):
        if (l[j] == r or l[j + 1] == r) and (l[j] != l[j + 1]):
            if l[j] > l[j + 1]:
                print(j + 1)
            else:
                print(j + 2)
            break