You are right about the atomic radii often quoted in chemistry, but the sizes of subatomic particles are usually defined in ways related to their cross-sections.
But isn't the cross section dependent upon what is interacting with them? Like, my understanding is that the cross section of hafnium is massive with respect to neutron capture, but not with respect to photons.
Although the size isn't simply the square root of the cross section, you've hit on a truth that you'd get different sizes if you were asking about the distributions of different things.
