I'm going to once again try and proliferate the term "side check" on puddle jumpers and regional jets vs the term "gate check". To me, a gate check is when you're on a mainline aircraft and you have to hand in your bag to the flight attendant, they give you a claim ticket and at your arriving airport, you need to go to luggage and wait a half hour and claim it.
Side check is where you drop it off at the side of the plane before heading up the stairs or on the jetway. You put a green tag on it and, on arrival, you wait plane-side or on the jetway for it and you get it there.
There is more confusion with in-frequent flyers on the whole gate-check nomenclature, we need to have a standardization on terms.
For the OP, on either the 145 or 170, plan on a "side check" where you drop it off when you hit the aircraft door and pick up outside. You may get a 22" on a 170, but it just depends. Definitely not on a 145.