RPS
I am guessing the Brize controller wasnt busy so by giving you the Cotswold and not his QNH/QFE to transit his Zone, thus saving you another pressure change on leaving. In that area I believe you are in the Cotswold RPS? So at WCO change to Luton and get either their QNH or London RPS. Its not really an awareness problem whey should a BZN controller worry about your altitude on crossing the Luton CTZ? In a GA plane WCO to edge of Luton zone is plenty of time to adjust if you give Luton an early call.
Benson usually give the Cotswold when tracking towards CPT because 8/10 times in previous experience pilots GH to the west of CPT in the Cotswold RPS area! To the east of CPT they will give you the London RPS or at least I would expect them to. QFE when flying next to mil aerodromes helps co-ordinate you against IFR traffic inbound. Our Mode C readout is always based on 1013 so at least with a/c on QFE its easy to work out internal co-odrination rather then a long winded call right so your on the Cotswold im on QFE .....waiting to work out differerences do I have enough separation when your planes are getting closer! Most of the time its pretty easy but when your busy it helps. Im off for a ly down pressure questions do that to me!
Happy Flying
NM