Hi - this might be a known issue, but I couldn't see any other threads discussing it.
The interactive renderer doesn't update correctly when working with fields in R20.
I've attached a scene with a simple setup (a cube in a cloner object set to array, with a plain effector modified by a linear field in the falloff). When the IPR is launched, it initially renders correctly. If you then change just about any parameter in the effector or the field, the IPR ignores the field and applies the effector to all the clones.
In R19, the IPR seemed to work fine with falloff.
I'm on a Mac Pro running High Sierra 10.13.6, with C4D R20.059 and the Corona Daily Build from 27th May (core 4 (Release Candidate 1)). I was also having the same issue with Corona 3 - Hotfix 2 and I think Hotfix 1 as well.
Cheers!