I don't know, I'll play devil's advocate here. Starting at 4 1/2" of reflex I'd expect you could retain 1 1/2" of the without too much being outside the statistics. More than that under ideal conditions. I feel ok about a project if the bow takes 2" or less of set start to finish. A lot depends upon the design, crafting, materials, humdity, etc.
That said, I don't find finished, shot in bows w/ more than 1" of net reflex particularly desirable. You get just a shave more cast w/ more than that, but all that honkin' weight at brace height means your still "steering" the arrow at near full throttle at the bottom of the power stroke. If one is wonton to do a few of the stupid shooter tricks (speaking of myself here), like droping bow arm, relaxing bow arm, etc., it means yer arra goes just the more in the wrong direction.
That one looks like a nice project. Be extra cautionous about making draw weight, but don't fall back to the lazy man's approach of just working all the goodie out of the stave during the crafting to accomplish shame. If you want to dial it down some, use heat before you start rather than crushing wood to change the profile. Should finish w/ a real humdinger.
