First of all, you must realize that it is normal for the foot-operated
sustaining pedal to lift the dampers higher than the pneumatic device.
In most players, the sustaining pneumatic is slower to close and slower
to open.  If it lifts the dampers too high, the dampers may not have
time to do their job before being called upon to go up again.

The proper height limit can be as little as an eighth of an inch if
all the dampers lift the same amount together.  But if some dampers are
still resting on the strings while others have adequate clearance, you
will need more travel to get them all off the strings until a piano
technician can make things right.  If the dampers seem fairly
well-adjusted, try 3/16 inch for good measure.

Normally a grand piano action does not have a hammer [rest] rail;
that is usually a player innovation borrowed from the upright action,
although some non-player grands will have it in place of the action
shifter.  When the grand hammer rail (if there is one) goes into the
soft position, the keys will drop (with the possible exception of a few
in the extreme treble).  This means that the weight of a key may
interfere with the normal action of its corresponding damper -- a point
to be considered when regulating the dampers.

I've observed that in many player and reproducing grands, the keys will
lift the dampers higher than the well-adjusted pneumatic sustaining
pedal device, but not as high as the regular pedal.  This is okay,
because the human foot is many times faster than the pneumatic.

Jeffrey R. Wood