Idea of photophoretic force enhancement by channels and macro pores, a) low pressure: only the real cross-sectional area counts, individual molecule collisions and momentum transfer; b) intermediate pressure: thermal creep in channels leads to increase of pressure at warm side; c) high pressure: thermal creep only acts close to the inner channel walls; pressure increase can be balanced more easily by back flow through the center part of the channel; d) thermal creep in more realistic porous bodies in protoplanetary disks (dust aggregates, chondrule aggregates, larger rubble piles).