Keith,
The N20's mainsheet blocks hang from the boom to the rear cross beam at such an angle that when you sheet in, it forces rotation by pushing the boom forward. The F18 is more vertical and pulls more down than forward. Anything more complicated isn't really needed.
Understand/know the geometry thing. It stands to reason it happens easier without the lines all over the boom/mast. Still seems like you need something to lock it in, or in some cases force it, depending on conditions. Although effective I dislike the lines on the boom to force/lock rotation. Was starting to think of something like Todd is suggesting. Sounds like it's time to change the base and experiment!
