Where you tend to sit on the saddle can be affected by all sorts of factors. Tilt, reach, your body angle, how much power you put into the cranks and I'd suppose how wide your saddle is.

I wouldn't worry about pushing yourself off the back of the saddle. Why will you want to do that? I can pull myself off the front of the saddle, but I don't.

Might indicate that your body is willing to be stretched out a little more but I don't know from any knowledge, I'm just supposing.