This is a two-part response.  The first part is based on my experience.

I have had two good rebuilds ruined because of high humidity which
caused the pouches to shrink so much that they floated the valves.
In the case of the Ampico the customers house was so damp that after
a few months there was mold and/or mildew growing on the inside of the
belly cover and on the twill covered hose.  In both cases I had put in
new leather pouches with plenty of dish at the time of installation.

Unless I am sure the piano is going into something like the Mrs. Mega
Bucks museum where there is precise climate control I would much rather
have a little extra dish than chance having to redo the pouches.

I have noticed that when I open up the pouch board on an old player
that the pouches have only traveled enough to let the valve seat in
its at-rest position.  The pouches do not go to their full travel.  Based
on this I do not think excess dish would make much difference.

My own personal opinion is that there is more cause for concern in the
rebuilding of the piano action itself.  I have seen several good player
rebuilds that didn't play well because the piano needed help.


The second part is presented as pure speculation and "dividing rabbits"
("splitting hairs"), and as a thought game.

If you are worried about fast repetition, should not the pouch be
dished so that it almost reaches the bottom of the pouch well, and the
valve stem be extended so that the pouch is at the bottom of its travel
in the at-rest position?  This would leave a smaller volume of space
under the pouch and it would take fewer molecules of air to raise the
pouch.

Shouldn't the opening for the tube from the tracker bar be under the
center of the pouch so that the air rushing in would lift the pouch
evenly and not more from one side?

When recovering note pneumatics should the cloth be just wide enough so
that the sides are straight when the pneumatic is open?  Or should the
cloth be cut so wide that the pneumatic looks half collapsed when in
the open position?

With the narrow cloth, the leaves will make a greater movement for the
same amount of movement of the cloth, but with the wide cloth there will
be less air to exhaust to close the pneumatic.  What will be the effect
on power and speed from moving towards one extreme or the other?

John Dewey