The rest should reach its upright position only a couple of inches before you reach full draw. Make sure that you can still come forward 2-3 inches from the full draw position before the rest starts to move downwards. If the rubber is too tight, then the rest may not drop away in time and you can still get the arrows striking the rest.
I've taken this information from an article, maybe it worth checking this out.
Tuning will take some time, so relax, avoid frustration and enjoy what you're trying to achieve.
You can also check if there's any side to side movement on your cam, this is another area that can cause bad arrow flight. Seeing that your bow is a single cam-- you can eliminate cam timing problems.