To realign the garage door blocked-opening sensor beam to keep the existing low level
sensing and add bumper-height sensing, with a Z-shaped sensor beam (A, B, C, D),
add two small mirrors (B and C), as described below (or some similar variation):
Call the original sensors A and D.
1. Move just one sensor (D) up to "bumper height".
2. Add (*) a small flat mirror (B), where sensor D was located.
3. Add (*) a 2nd small flat mirror (C) above sensor A, at "bumper height".
4. Align each mirror so that it faces the point exactly halfway between
the opposite-side mirror and sensor.
5. Check that breaking the new Z-shaped sensor beam works, both
at the original low level and the new "bumper level".
(*) Adding an additional mount similar to the sensor mounts might be
difficult, and the original mounts might not even be adjustable. So,
adding a vertical extension to each bracket, up to "bumper height"
might be easier. Some ingenuity might be required.
Cheers, Gary