Even with my 8:1 mainsheet, when fully tensioned, the boom displayed an annoying upward flex in it. I can only imagine what the 10:1 blocks will do.
Is there any particular reason that the sheet point is behind the clew of the main? Does it help keep the roach/square top tight?
Having it that far back certainly seems to stress the boom moreso than I would have thought. But I guess that's part of the design, too...?
You have to have the mainsheet at a slight leaning angle so it applies some compression on the boom to push the mast and keep it rotated. Several I20's came out where the mainsheets attached with a strop to the mains and you couldn't keep the masts rotated.
