I’m trying to diagnose what tuning I need to get a smooth top layer on a solid print.

The picture you see is a 50mmx50mmx1mm square (cube([50,50,1]); in openscad) printed with a .4 nozzle. (5 layers)

For tuning on the problem, I have looked into:

• z_offset – tried all kinds of values and if I reduce it anymore, it doesn’t squish into the bed and the center part is exactly 1mm – so unlikely to be that.
• bed level – bltouch is working well
• extrusion (esteps or rotational_distance) - played with this a great deal and any less and i start to have under-extrusion in the center area.
• different filament – same with PLA, PETG and ABS
• Different slicer – same with PrusaSlicer or Cura
• Different speeds – one on the left was printed at 20mm/s – the right was printed at 150mm/s

I also cant find any guides out there that show this issue. Anybody with some suggestions or threads I can pull?