Air Assist ‘on’ makes the line less distinct

I have a 10W Grbl laser (Creality Falcon) that I have used to engrave some lines in 3mm birch. The layer is set to 1000mm/min and 80% power and the air pressure is set to ~50% (manual assist), because I’m not cutting.

When I run the job with Air Assist off, the line is clean and sharp as seen in the picture, as opposed to when Air Assist is on where there is visible kerfing and corner artifacts. Is this normal, or am I doing something incorrectly? It’s pretty much the opposite of what I expected, and I’m not sure what’s causing it. I did remove and check the laser head, in case something was loose or dirty, but it looks fine.