Give it a shot. In truth, the degree of "flatness" (due to
sheet tension) is but another of the
many (too many?) available sail trimming tools. It's a fact
that the WWP19 sails best in moderate winds if sailed both
"free" (in the sense of having full rather than flat sails)
and "loose" (in the sense of heading off a bit from the best
achievable upwind angle), but when the wind pipes up flatter
sails help reduce heel. Varying the twist is also a useful
technique to deal with varying wind ranges. I use the
adjustability inherent to the genoa track a good deal, with
any headsail except the spinnaker. [There are those who'll
say the above should be "loose and free," rather than "free and loose."
I don't know which, if either, is correct.]
My nominal headsail remains
the 150% genoa. Using it with varying degrees of twist and draft
and a full, single reefed or, double reefed main, you're good for
upwind work in 3 to 20 knots of wind. The last step is to drop
the genoa and run away somewhere under double reefed main alone.
With a jib downhaul, you are ready for anything -- except going to
windward in 20++ knots, an ugly enterprise in any case -- without
ever having to go to the foredeck.