On my 23, I mounted a six foot long bimini to where the trailing edge is just a few inches in front of the back stay. In hindsight this worked out in our favor - it is good to have a little room behind the top, to allow for standing up at the very rear of the boat. This really helps when using the boarding ladder or if someone is trying to hand you something off the dock. Also the bimini adds greatly to the enjoyment of the boat. Good luck.