That is exactly what your problem is.
Blocking the eye constantly causes an eye error, so the board reverts to the 8bps rate of fire that you set.
Blocking the eye constantly does not trick the board in to thinking that there are balls loading - in fact, it tricks the board in to thinking that there is a problem with the eye. If anything, blocking the eye is more like having paint on the eye than anything else.
Normally, after the marker fires, and the bolt retracts, there is a brief period when the breech is empty - the bolt has opened, but the next ball has not yet dropped in to the breech. The eye sees that the breech isa empty, and passes this information to the board. At this point, the board starts waiting for the eye to see a bal fall in to the breech. When that happens, the board knows that the marker is ready to fire again.
If the eye never sees an empty breech, the board doesn't know when the bolt opens or when the next ball feeds, so it assumes something is wrong, and drops your rate of fire.
The eyes just don't work properly unless you are shooting paint. If you want to dry fire or just click the solenoid, you need to turn the eyes off.