Nebbian in the Delta forum has a theory that the "tree ring" patterning seen on delta printers might be due to the drivers missing a step at the transition from slow to mixed decay.

[reprap.org]

I was looking over the A5984 and A4982 datasheets, and they have a mode called "APFD" which is turned on by grounding ROSC. This should keep the driver in mixed decay.

Based on the schematic on GitHub, Smoothie v1.1 boards don't ground ROSC. Is this correct?

Did you guys ever experiment with that?

I believe a few people have tried that and some have seen improvements, others not. So probably worth trying, but YMMV.