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())
    a = list(map(int, input().split()))
    m = max(a)
    if(a.count(m) == n):
        print(-1);continue;
    u = 0
    for i in range(n-1,0,-1):
        if(a[i] == m and a[i-1]!=m):
            print(i+1)
            u = 1
            break
    if(u!=1):
        for i in range(n-1):
            if(a[i] == m and a[i+1]!=m):
                print(i+1)
                u = 1
                break