Since writing the book, I have come to realize that a 24inch level cockpit is borderline for the six foot paddler and prohibitive for anyone taller.
Leg length is actually the real culprit that make getting in and out of a kayak a challenge.
First of all, the position of the deck beam at the back of the cockpit is the right place for your back to be when you are paddling. You can probably move an inch or two forward or backward without affecting trim and handling adversely, but too far off may introduce problems. I had the pleasure of seeing boats built by Jim Mitchell in Seattle. His approach was to extend the cockpit in back to make entry and exit easier. But instead of using the back deckbeam as a backrest, he used a commercial strap in backrest lashed to the ribs.