When leaving from non Heathrow stations then it does help to NOT checking at a terminal, it's often these smaller stations that can have the station manager assign an upgrade, if you are checking in at LHR then it doesn't matter, if you are being upgraded then it will happen in advance anyway...

If you don't get an op-upgrade then make sure to mention that in the F lounge at LHR and ask the agent behind the desk to keep an eye on any moving around of seating assignments and that you'd be happy to move "up front", don't use the U***** word...