A couple quick thoughts, first and the easiest, reefs are almost always cut so that the aft end of the boom is higher when the boat is reefed. You need a fairly large gap between the boom and the traveller when the mainsail is fully tensioned. The reality is that the leech of a mainsail stretches quite a bit in a strong breeze and you need to be able to pull the aft end of the boom down in order to take that stretch out of the sail and reduce heeling. There will be a small amount of deflection in the arch and traveler and since you have mid-boom sheeting, the boom itself will deflect as well. Cumulatively these combined factors could mean as much as a foot to 16" difference between the vertical position of the block with the boom at its normal sailing height and when hard on the wind in a strong breeze.
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Curmudgeon at Large- and rhinestone in the rough, sailing my Farr 11.6 on the Chesapeake Bay and part-time purveyor of marine supplies