thank you for sharing,,
the bow was probably designed to shoot at 23 or 24 inches of draw,,
that would put you 48 ish,, maybe a little more if the bow is stacking a bit,,
the power stroke at 23 or 24 would have much better cast,, if the bow had been shot at that 24 inch draw before,,, it now would put it at real disadvantage shooting it at 20 inches,, it would just not shoot well,,( that may be why the cast seems a little slow)
you would be getting about ,,,, 150 fps with 500 grain arrow at 24 inches maybe more depending on how much reflex the bow is holding unbraced,,with the lighter arrow you had, it will really be zipping,,
most guys that make sinew bows ,, design them to draw half the bows length,, and some further,,
as far as the appearane of the tiller,, hard to tell without seeing the bow unbraced,,
but one thing is for sure,, if the bow is a bit whip tillered,, it may not be shooting its full potential,, or if the tiller does not match the design or lenth of the bow,, it may or will not shoot as well as it could with a different full draw profile,,