Need help - Attractor Grid + multipoint

Hello everybody,

                       I'm a beginner with GH and I managed to complete a curve attractor grid of circles. I managed to set a value for the diameter of the circles so that they don't overlap. But I also want a minimum diameter for the ones near the attractor. In other words, I don't want them to become infinitely smaller as they get nearer the attractor.

What must I do?  

Thanks!