Jon,  The maximum opening distance (total fabric width) for the
regulator and re-regulator pneumatics is usually 1.50".  In practice,
it is not critical if that opening distance varies just a little,
since the main regulator pneumatic (the one with pressure controlled
by the crescendo unit) is adjusted so the connecting rod limits its
travel to about 1/8" total motion, with the pneumatic never approaching
its fully open or fully closed position.

The spring pneumatic operates only when in "Subdued" mode, where the
spring tension and connecting rod length should be adjusted to reduce
the maximum stack pressure to 10-12" rather than the normal 20"
un-amplified maximum.  Again, the exact pneumatic opening doesn't
influence its function that much.

Best regards,
Ralph Nielsen
http://www.historicpianos.com/