Richmansbmw

Hi all. Had my 55reg for a few months now with no real issues apart from two new air bags at the rear. It's covered about 138k miles so didn't do too bad I guess. I'm in the process of researching tyres, as it's running snow tyres at the moment on 19" wheels. But making a noise that I'm hoping isn't the transfer box. So thought to treat her to a new set of tyres just incase of uneven wear.
Anyhow the reason for this post is the rear seems quite harsh or stiff even when in comfort mode. The front seems fine though. Is this just the characteristics of the car or did the fitted not do something correctly when fitting the new air shocks.
Any advice or thoughts welcome. Thanks in advance.