If you selecting the size of your envelope as COM10, your going to have issues.
You should set as CUSTOM SIZE POSTSCRIPT,
set slightly off the size of COM10, so i usual do 4.13x9.5, if you do 4.12 it will know its a envelope.
Then set speed the LIGHT MEDIUM to start, that should pull it a lot faster so you don't have the issues when telling it a COM10.
also some business flaps you have to run inverted. But we don't have a feeder, we run out of the bypass, i couldn't justify the cost at first for the feeder, now i am thinking about it.