I have what might seem an odd first step suggestion for grand regulating: Pre-lift wire. This is a strategy to end up with no underlifted strings.

When a piano is newly strung, the steel wire, being stiff, takes rounded curves, not corners, as it passes bearing points. Each time the wire is pitch-raised it refreshes these curves a little, particularly at agraffes and Capo D’Astro bars. A conscientious technician will settle the wire and mate strings with hammers, a process well-known to us all. Touch hammer to unison strings, pluck the strings, and if any ring, lift the others with a stringing hook until all are equally muted.

Q. Thoughts on aftertouch affecting checking?  A. Aftertouch directly affects backchecking. If we define aftertouch as key travel after letoff, this can translate to backcheck travel after letoff, since the backcheck is attached to the key. Further key stroke equals greater backcheck reach and less equals less. Imagine no aftertouch. The jack ...