In this application the radiation pressure is pretty minimal yeah. I haven't seen numbers for it myself, but in some other settings where you care about direct radiation pressure & ablation pressure, you usually discard the radiation pressure term entirely unless you are very close to the source or it's an incredibly potent source. For instance, in Teller-Ulam type thermonuclear bombs, the radiation pressure from the fission stage is assumed to provide virtually all of the implosion pressure for the fusion stage [going by unclassified sources only ofc, e.g Winterberg "The Physical Principles of Thermonuclear Explosive Devices"].