I agree with the comments made by Mark and A Former User. I can add a little from the real aircraft perspective.
The altimeter system (unlike that of the RJ) is obviously more prone to variations of holding altitude with speed changes/temperature and power changes. The research aircraft at Cranfield has, as I understand it, undergone been modification to use the RJ sensors to allow RVSM operations- but I doubt that was cheap to do! I guess they can get up above 146 operating altitudes as it’s not carrying 112 pax.
146 type: Having captured (say) FL 280, the ability to maintain it varies with change of speed; slow down a few knots/M and it will descend slightly; increase speed and it will climb slightly. Speed changes may be the result of warmer/colder airmass and subsequent N1 increase or decrease, as well as fuel burn and a reduction in a/c mass. How much climb or descent? Some a/c were better than others, but typically 50’ to 80’ from required altitude. We had a form to fill in an advise the engineers if we thought it excessive. We would record parameters such as OAT (or was it TAT?), Fl, speed/mach, N1 and captured altitude and variance. They had a BAe doc to compare to and decided if it was acceptable or not.
To recapture the assigned FL, most pilots used the sync button. Very few used the pitch UP/DOWN on the rear of the centre console and ALT capture - it was so prone to under/overshoot.
I’m happy when I have the time to answer other 146/RJ questions if I can. But, we will fall out if you keep calling the thrust levers ‘throttles’. Cessna like to use ‘throttle’ for their jet - but BAe do not.😏