This was reported for the special case of mapping with "Strand / Particle" coords, but was not working with other coordinates either. Dont see a reason for not supporting Size influence textures for these kinds of particles (and since these types of particles have an "age" like all others as well, even the "Strand / Particle" coords are supported here as well) Maniphest Tasks: T88715 Differential Revision: https://developer.blender.org/D11449