In ramp mode (not PSP mode), the rate of fire actually increases in relation to your trigger pull rate, rather than just jumping to a set rate of fire. The ramp percentage is the amount by which your rate of fire will increase over the trigger pull rate.
So, if you have a setting of 50%, your rate of fire will increase by 50%, so 5pps becomes 7.5bps, 10pps becomes 15bps and so on. If you had a setting of 100%, 5pps would become 10bps and 10pps would become 20bps.
It is normal for only the emitter to light up and not the receiver. If the receiver lit up, it would see it's own light, rather than the light from the emitter, and would never know if there was a ball in the breech or not - a ball in the breech would not stop light getting to the receiver.