Top Layer Field Quality

Ender-3 S1
Slicer: Cura
Material: ABS
Tip: .4
Temp: 240
Bed: 100
Layer Thickness: .2
Speed: 50
Cooling: off

Have been struggling to remove a specific roughness in the final top layer. Just inside the perimeter wall, which is very smooth, I have clumping/roughness that fades towards the center of the print. I've been adjusting top layer thickness (which helped) top skin, extruder temp, top layer pattern and a few other settings specific to the top layer. If I didn't know better I'd say it's related to the decel/accel of the extruder as it changes direction but not sure. Looking for another body of knowledge....mine has run dry. I'll attach pictures that should show the issue pretty well. Especially samples 1 and 2. These are about the size of a standard domino.
Thanks, S.


Attachment 18312 Attachment 18311

Some pillowing visible, maybe try for three or four top layers instead of two ?

I'm at 5 layers now at .2mm layer thickness (1.0mm top layer total thickness). Referencing examples top layer thickness:
1. 2.0mm
2. 1.0mm
3. .75mm
4. .4mm
After adjusting top layer thickness I moved on to other settings. The thinner layers did help better than any other single adjustment, however the infill pattern began to show through (sample 4). Grid infill with 1.0mm top thickness was my compromise. I might revisit but I'm going to try a Monotonic order and maybe Ironing next.

Monotonic on, still at 1.0mm top layer thickness. Better, it really looks like it's dragging or over extruding at the beginning/end of the diagonal runs (every other run? hard to tell). I'll live with this for now, might need to tweek speed/extrude rate/z height to optimize further. Would love ideas/input on what might help. Again, very thin top layer thickness was the most dramatic improvement. I'm very happy with the Ender-3 S1, it went together effortlessly and was 2hrs from opening shipping box to acceptable parts.
Thanks, S.
Attachment 18314 Attachment 18315