UX is my primary mode of travel on United.
On the 135/145 you gate-check anything bigger than a backpack unless it is soft sided (duffle).
On a 170 (two cabin) the overhead for F will fit 4 22" bags. The overhead in Y will fit a 22" bag but you are taking up two pax overhead space. I realize most people only care about their luggage but taking up the binspace of two people is rude, IMHO. Some 170s operate out of combined RJ and standard berth, so when you leave your luggage may or maynot arrive via gate. I know when I leave CMH for ORD, it can be a crap shoot. Make sure you ask, and verify the green tag.