I don't know what radar's you're using, but all the NATS radars I've used for 34 years are configured to show altitudes below the TA and FLs above it, so where's the problem?
We used to have one system at my unit which was configured to accept different QNH values where necessary ie observed QNH under the TMA with TA 6000ft and RPS outside it with TA 3000ft.