Why would anyone want to apply carb heat in the hover ? You only need carb heat below 18".
Robinson Safety Notice 25 says
... apply carb heat as required during hover and takeoff to keep CAT gage out of yellow arc.
So "keep out of yellow arc" (and current advice appears to be a more conservative "keep between 10-15 DegC"), unless below 18 inches MAP in which case ignore DegC and apply full carb heat.
RC