HI Nikita,
If I remember correctly, each Particle only interacts with the one closest to it. With variable Radii, it is of course possible that a Particle collides with another Particle that is not its closest neighbor. If the Radii variation is large, then that will happen more often than with a small variation.
So, yes, you could do more checks per Particle per Frame (probably by using a Repeat Zone, as you indicated), but the question is, is it worth it? It’s a bit of a balancing act, between calculation time, accuracy and stability.
