Funny how the information kind of dribbles out in this thread
You are saying that when you are ALONE and sit in the rear seat, the boat is out of trim balance, which is perfectly understandable. If you substitute a shorter tiller, sat in the rear, AND had a passenger up more forward (middle seat or even farther forward), how is the balance then?
If two passengers, properly distributed, is not too much for the boat under the conditions you expect, AND you can safely steer with a short tiller from the rear seat, then you may want to consider an easily swappable tiller system. Use the short tiller when two are aboard and the longer tiller when you are alone sitting in the middle seat.
Hope this helps.