The smart Money is to try and ask, very Nicely if Pete B when next at lambourn can take a look at it for you.
My thoughts are that your engine has been tuned whilst cold.
it needs to be tuned whilst hot as that is how it will fly.
it is common for revs to be higher on a cold machine, lower when the same unit is warm.
The fact that the revs change between hot and cold should discount the prop as the problem
Cold air in a cold engine runs leaner, than the same settings when warm.
If I had to guess its worth checking if the top end is too rich, Pete may well say this is Baldwindash
Pete is to tuning what Christine Keeler is to high class hooking