Warm air carries the particulate upward
Heated air rises, and it carries with it whatever is suspended in it: cooking oil aerosolised from a stove, soot from a fireplace or candles, dust, and combustion residue from gas appliances. Drapery hangs directly in that rising column and behaves as a filter. The particulate meets the fabric and stays, and because the flow is strongest near the ceiling the deposit concentrates in the top third of the panel.