Eric, as Tom said. Furl as much as you think you need (ignoring what that batten does), cleat the furling line, and then adjust the mainsheet to get the right shape of the smaller sail area. I tend to just leave the downhaul cleated at the same position all the time (tight enough so that there is a very slight vertical crease when there is no wind or tightness of the mainsheet). I know that theoretically I could improve the performance of the sail by varying downhaul tension, but I simply don't bother.
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