mine stands at about shoulder height on a chest of drawers, just like its predecessor. so far, the ceiling hasn't let anything show. however, it is conceivable that something could settle there, even if this technology does not generate excessive localised humidity, as it is supposed to. in any case, you would see it coming for a long time. in any case, the performance does not seem to be affected.

I have it on the floor

I don't think that matters. Can be placed on the floor or on furniture. Just keep a distance of about 1 metre from the furniture/ceiling above the appliance because of the moisture that occurs