I fly a lot on older Russian planes, and you can get a lot of engine fumes which always seem worse at the back.

I recall a DV trip GYDBAK on an AN24 in October 2007 when the fumes were almost choking point - if there had been functioning oxygen masks, I might have asked for them to be deployed. At least noone cares on DV if you use your mobile phone in flight....

Plus TU3 is definitely bumpier at the back even in clear air.