So after a lot of trial and error and learning from my mistakes and the help from Allan from Fre-E-Target to understand better how the system works...
I fine tuned my sensor locations using my 230mm guide:
I then reconfigured my target frame to have the impact area as close as possible to the sensors and used a flat sturdy floating metal plate.
I shifted my aiming bullseye to the front of the target frame similar to what is used for Sius and megalink targets and illuminated with a pair of battery powered task lights...
The resulting accuracy was what I was originally hoping for.
Things to fine tune further:
1. Pellet trap metal is still not quite sturdy enough. I can see after only 20-30 hits it started to bulge a bit. I may have to switch to proper hardened steel rather than thick sheet metal.
2. Pellet debris is bouncing forward a bit into the box/frame. A better pellet collection may need to be designed or just allow the debris to collect in the frame and dispose after each session. Messy but should not affect the sensors at all.