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

def main():
    for _ in range(int(input())):
        n=int(input())
        a=list(map(int,input().split( )))
        s=set(a)
        if len(s)==1:
            print(-1)
            continue
        index=-1
        m=max(a)
        if a[0]==m and a[1]<m:
            index=1
        elif a[n-1]==m and a[n-2]<m:
            index=n
        else:
            for i in range(1,n-2):
                if (a[i]==m) and (a[i-1]<m or a[i+1]<m):
                    index=i+1
                    break
        print(index)
main()