I didn't see 4pie's post before I responded. The photo he shared showed the pitcher finished with his "chest" down, which helped push the ball down. I am not sure if you (tatoforver) are doing so already, but it's possible that you are not. It kind of echos what I said about the angle of the arm release, yet it's slightly different.
I learned to keep my mechanics consistent (or the same). I control my release slightly in order hit the corners (1, 3, 7, and 9). I am not saying it works for everyone, but when I practiced alone with the net, that's what I did.
One of my son's pitching coach just wrote a nice blog, http://www.lockedinbaseball.com/blog-1/
This is what he wrote:
That’s why I have my pitchers throw 4 different throws:
Normal pitch from the stretch
Just something to play with.