UA's CRJ700 OH bins are small in terms of heights - something like the B&R 250X unexpanded will easily fit mainline jets, even when slightly expanded its 7.5" specs - and, of course under the seat in front of you. The newer CJR700 have a bigger bin opening, that is quoted as up to 10" but Mrs. L's 22" roller and my soft 22" Mother Lode/TLS weekender is usually tagged & left at the jetway door checked anyway.

If you are flying F, GA/FA should leave you alone & they are focused on gate-checking all the bigger carry-ons (i.e. all those "regulations-sized" 22 inchers just won't go up there, too narrow or tight to fit thru) There is very limited space onboard to store these rollers, so practically everyone is asked to gate-check the bags, except for regular briefcases & large totes. Beware that you'll find some of the OH bin space already taken if you are among the first group to board (by FA/crews since they are also storing theirs ...)

Besides, depending on load factor, they ofen must do weight balancing & often move pax around to redistribute for take-offs.

If your laptop is a sleeve, pull it out for boarding to make it easier - as 9" will not fit up there. Here's link to a photo of UA's CRJ700 - http://www.flickriver.com/photos/caribb/85819514/