GEM position (cem120) to determine the height of the GEM related to wall height/pier height for nexdome confusion?

[theskyisthelimit99]

This is my first GEM, the cem120.  I've literally just unboxed it and set the latitude.  I was given the stat from ioptron for 40.5 lat. that its about 9.40 in height from the mount plate to "center of OTA".  Now i'm trying to confirm this.  I'm not sure what position that stat comes from, is it the "parked" position, zero position, counter weight straight out (not aimed down) one?

What i'm wondering, is if i change telescopes (from 8se) to say edge 11 or even 8se with a piggyback refractor, that height is still considered 9.40 to center, but center of where exactly.  How do I target a 53" wall height (and adjust my pier that i'm creating, concrete in the process)?  If adding piggy backed equipment really has no barring on that wall height position, then I guess i can just go with 53-9.40 to get the pier height I need to make and not worry about things being too high?

Thanks in advance for any clarification