Funny.....I did the same thing on my new Giant Escape 0. Today, after about 10 miles, I was feeling a little uncomfortable on my seat and "scooched" back just as far as I could out over the seat. Wow, my leverage was perfect and the comfort was the best I felt on the ride......BUT, no support back there.

The bike is new and i am still making small adjustments. Now the irony is that just yesterday i had my seat further back in the position i was riding today with my ass out over the back of the seat and it wasn't comfortable at all. I just may have to try a different seat but I want to give my present seat more of a chance. I would like to try a Brooks B17 as I hear so many positive remarks about them. Or maybe just ride with my butt out over the back of the seat and call it good. I bet it looks hilarious from behind me.