Feedback on saddles which sit you deeper back with leg set a litlle more forward? 

Allen Ranch Saddles 

Martha Josey saddles has the forward hung stirrups. 

Bob Marshall treeless

Check out Horse Tack world!  Deep seat and your feet are out front! 

I had a saddle customized to hang the stirrups more forward.  Just by doing this is sat me back more.

Do you find that the HTW saddle slips? I've been hearing great things about the HTW with rider position but also hearing they can slip?

I have two Deb Sibley saddles.  One was ordered new (standard) and one I found used (7").  I love the fact that you can adjust the stirrups to be forward, slightly forward or hang straight if you like.  I prefer the forward hung stirrups that sit you deep and feel very balanced.  I have used these saddles on a variety of differentl built horses and they fit every time.  The flex tree feels like you are riding in a treed saddle, but I can feel my horse under me. I tried a couple of treeless saddles and didn't care for them.  

I've ridden both free runners and push style horses with these.  With a push style, i feel like I can get up and forward when needed, but still secure when they rate for the turn.  With the free runner, I felt just a secure and deep in the seat. They are pretty lightweight and the leather quality is very good.  

I've had 3 different friends who ride in HTW saddles and they all sold them after not having them for very long. 2 of them sold theirs because of issues with it slipping

I love my Josey saddle with the forward hung stirrups. I will say this. I didn't like the saddle at first and it was not very comfortable until I moved the stirrups up and down to find the "sweet" spot. Once I did this the saddle rode so much better. Also make sure with any saddle that you get a big enough seat. A small seat is not what holds you in. It is your weight in the stirrups. If your seat is too small it is going to throw you forward and you can't sit back.