This is indeed an interesting discussion.  As a piano technician I am
often asked by customers to even out or lighten the touch on pianos.
Usually this is customers with grand pianos, but it can apply to
vertical pianos as well.

While it is true that the hammers in a piano are much larger in the
bass than the treble, in a well regulated and designed piano there
should be only a slight difference in the touchweight measured at the
front of the keys.

For years manufacturers have used a touchweight that measured somewhere
in the neighborhood of 50 to 52 grams to cause the key to move downward
in the bass.  Customarily this is tapered to around 48 grams in the
treble.  At the time player grands were being manufactured these standards
would apply.  To accomplish evenness in the keyboard lead weights were
added to the keys at appropriate places.

In recent years a lot of study has been done regarding touchweight
analysis and the way it is measured has also been refined greatly.
The question was asked if the key takes more force to move if lifted
from the underside at the back than pushing down in the front.

My guess is that it should take more force to lift the key from the
back than pushing down from the front.  However let me say that I have
never measured it to say definitively.  All things being equal, the
force should be consistent from key to key and the same tapered force
should be needed even when the key is lifted from the back.

I would surmise that this is indeed the reason for the graduated
lengths of pneumatics.  The assist springs being either removed or
altered on some player actions would only speak to greater degrees of
refinement in the actual use of that particular action.  This would
compensate for slight irregularities in both the player action and the
piano action as well.

Addressing friction at every point along the way goes a long way in the
touch of the piano action.  It is also equally important to have a very
well regulated piano action to really enjoy the nuances of any
reproducer.

Norman Cantrell