I sure hope I'm getting this correctly. If we increase the brace height,
we would be using a shorter string than before. That means at the
original draw length we would be pulling it harder than before. In all
wood self bows the increased draw weight at the same draw length might
not be enough to compensate for the loss of the stored energy that was
available with the lower brace height.
TBB vol.4 p.145 Best Brace Height
For a 70" stiff-handled bow best speed per draw weight is reached
with a 6" brace, measured from the neutral plane. Similar ratios of brace
height to bow length are approximately correct for shorter and longer
bows.
In that case, what would be the best brace height for a 48" bow? Does it
make any difference if it is a horn bow?
I'm guessing but the force draw curve of the higher brace height would
pass the curve of the lower brace height somewhere near the maximum draw
length. If you are willing to pull longer and harder, the stored energy
for the higher brace height might even surpass that of the lower brace
height. But probably never within the original draw length. No idea
whether this would apply to horn bows or not.