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())):
    x=int(input())
    a=list(map(int,input().split()))
    if len(set(a))==1:
        print(-1)
    else:
        r=max(a)
        ans=-1
        for j in range(x-1):
            if a[j]==r and a[j+1]<r:
                ans=j+1
                break
        if ans==-1:
            ans=x
        print(ans)
