All things being equal, including stack thickness, width at fades and at tips, and same front profile, I believe the shorter bow will typically need more taper.
In practice this will almost never matter because you're never going to have two bows that fit that description ...
My advice is if you really wanna try to calculate the proper taper, use supertiller. I spent 7 years studying engineering and I wouldn't waste my time bothering any other way, Especially for a wood bow ehere you need to have nice even stress along the limb so you don't get hinges.
If you don't wanna go the supertiller route, my advice is give yourself a little extra width on the bow and a little extra thickness on the belly lam so you're got room to maneuver.
I've found that with bows ranging from 58" and 1.5" wide, to 68" and 1.75" wide (all with 1/2-3/8" tips) that a good starting point is roughly .00125" taper for every .100" of stack thickness.
So if you're bow is going to be .500" thick immediately after the fade, then you'll want .00125" X 5 = .00625" total taper, or .006" total taper. You'll probably end up tillering a little more taper in, but that'll be darn close. I'd say it varies typically between .00125" and .0015" of taper for every .100" of stack thickness.
The takedown I just posted has a 22 or 23" working limb, the stack thickness is .450" at the fade, and the stack at the tip is .310" thick.
Thats .140"/23" or so which is a total taper of about .00625", which is .00138" taper for every .100" of stack ... so right in the middle of the range I gave you.