We purge ethanol in thin films under vacuum, using a hotplate inside the vacuum chamber, using a 6" Petri dish and 115F. As long as the film is kept thin enough, all that is necessary is to keep track of bubble production, so that we know when to stop.
In super thin films, decarboxylation also happens faster, so it is important to remove it from the hot plate when the large irregular bubbles stop and only the small fizzy bubbles remain, so as to retain it in carboxylic acid state.
I might posit that it is the vacuum that is accelerating the decarboxylation process (instead of film depth), as it also seems to hasten the CBN conversion rate...