May consider developing different challenging shot scenarios until you reach 20. Start with the inital ones and draw the scenario from a hat. Keep developing and adding challenging yet different scenarios.
Example: Run thru ten random scenarios in one pratices session. 1st drawn scenario - Walk quickly but quietly in lowered position up hill for 200 yards, belly crawl for w/bow for ~50 yards, duck walk quitely for 35 yards. Set back against tree w/ anticipated shot ~15 yards virtually directly behind you. Remain stationary for ~10 seconds. Draw to full anchor and hold near target for ~ 7 seconds then move on target and hold for three, then release. Target to be a blank paper plate with 2nd plate underneath with an 'X'.
Just a thought. May be fun - May be hell.