If it were me, I would set all the head-stops to their neutral position. Meaning that they are equidistant from either of their maximal ranges. Then back-off the positioning of the center most head-stops about half a turn or so, so that only the two outer most head-stops will be responsible for registering the sheet.
Place a sheet into the feed table and register it into the two head-stops which we discussed earlier.
Then adjust the sheet detector optics, moving them forward in the feed direction until they indicate a mis-registered sheet despite there being a properly registered sheet in the head-stops. Do this one at a time for each of the detectors.
This delineates where the detect/no-detect point is for the optics with respect to the head-stop positioning.
Now just move the optics against the feed direction until they detect a properly registered sheet in the head-stops, then give them another 1/2 turn as a margin.
Anytime you move the head-stops in either direction, you should also reposition the sheet detection optics correspondingly.
OT[/QUO
as posted earlier there is a very specific sequence for setting the optics. The detectors when set correctly should not require adjustment every time you make a headstop move. They should operate adequately throughout most the entire range of headstop adjustment without requiring them to be moved every time you cock the headstops.