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()))
    if len(set(l))==1:print(-1)
    else:
        m = max(l)
        f = 0
        for i in range(n-1):
            if l[i]==m and l[i+1]!=m:
                f = 1
                print(i+1)
                break
        if f==0:
            for i in range(n - 1,0,-1):
                if l[i] == m and l[i - 1] != m:
                    print(i + 1)
                    break