Hi Eliyahu,  Since you don't seem to be getting any responses to this
one, maybe this will help.  I have no idea of the positioning of the
subject pneumatic in the grand but, if the upright is similar, my piano
which has never had this adjusted since it left the factory, sets the
Accompaniment level to 4.  I tested this by collapsing Accompaniment
pneumatics until they reached the stop with the 88 pneumatic collapsed.
I think it took me less than two minutes.

In some ways I would actually prefer it to be a little softer but then
it could miss notes if big stuff came along and I was just letting it
run while I had breakfast. (Rather unlikely.)

I find it a useful feature as it sets the basic 88-note accompaniment
playing level at a mid point and the pianolist can conveniently push
the accompaniment lever left or right for softer or louder playing
rather than working from zero intensity.  The pneumatic acts as a
spring and not a solid stop.

Hope this helps.

Jim Heyworth,
Sechelt, B.C., Canada