Well I set it all up again on the lawn this afternoon, in the same stiff breeze. I had basically drilled the second hole in the boom (done the other day) too far forward. Really, it's correct in that it's where the reefed clew needs to sit, but actually it needs to be about three inches farther aft to make for a simple attachment which when tensioned up by the snotter comes to sit in the correct position. I played around with the sail height, just as John suggested, which also gives me a little more room for the downhaul as well as lifting the boom slightly.
I was then quickly able to set up a very nice very flat full main, and very flat and taut reefed main (I should have taken some snaps). The mizzen will have some fairleads and jam cleat on the boom. The main doesn't need it.
Unfortunately the reinforcing in the clew is way overdone, which makes it hard to fold up that corner of the sail when reefed. Also the clew is quite small, so I could never get it over a fork in the boom as Ross suggests. Likewise the cringles are on the small side but they won't produce any really problem. Those are lessons for the second set of sails.
Some changes I'm definitely going to make.
1. I'm ditching the lacing for webbing mast hoops, with side closing buckles. I will either use plastic shackles to attach them to the sail, or whip them on. The lacing is a pain, and a time waster. The web hoops make adjustment around snotters a piece of cake when raising and lowering sails for reefing.
2. I'm ditching nice hempy looking three strand polyester rope for braided rope. There is very little tolerance in my mast height and boom length to be able to get the adjustment I need out of stretchy rope. If I can find pretty coloured braid all the better. But I'm not buying any of that stuff with coloured fleck through it.
3. I'm going to hang my wood blocks on the mantle piece and replace them with light stainless blocks. There's hardly any load on anything on the boat, but the more small blocks I can get, the easier it is, with braided rope, to get everything taut.
4. I'm going to make some little separate cunninghams for luff tensioning.