I have a Hexagon 0.4mm head, and most my prints have been around 0.2mm layer height, first layer typically 0.3mm
The thickest I have tried is 0.3mm Most the photos are prints using 0.2 or 0.24mm
Far as I know, you should never use a layer height more than 80% of your nozzle width, so that would explain why your 0.4mm layer prints wont look good.

Yes, the artifacts are something else I am trying to troubleshoot.
It seems anywhere the head has to pause or come almost to a stop, it will leave a mark, or a very tiny blob.