what fill setting are you using?
I go with the Nozzle Smear Theory as well. Last image, look at the smear from the G to the 6:30 position on the logo circle. This appears to be a raster burn, text first, then up to the circle. The circle middle is smeared from one side of the circle to the other. IMHO, of course.
Sounds plausible, it doesnât look like the typical âover scanâ on both sides either.
I donât have any grey EVA, but I do have black, red, green, yellow, blue, & white. I can try some raster engrave on some this weekend to see how my machine behaves if this isnât resolved by then. Not exactly an ideal comparison, machine-wise, but it may reveal a material quirk.
Material tests are always useful and educational in my opinion and the result gives us new knowledge or updates existing experiences. 
By no means an exhaustive or definitive test, but hereâs what I gotâŚ
This was done in an enclosure with moderate exhaust airflow (200cfm, total enclosure air exchange approx 6x/min) and just a tiny bit of assist air (~4 lpm) that I use at all times to keep the lens clean.
.09-.10mm is my normal fill interval for wood. I could probably bump it up some for foam since itâs far less heat tolerant.
My laser doesnât regulate power/switching very well below 15-20% at speeds over about 2000 mm/min, so I didnât bother with anything below 10%, which should be roughly, what?, 6-7% for a 10W diode?
Anyway, I canât see ANY signs of smoke staining on top or bottom (I use a sawtooth bed).
I still think your laser is not reducing power properly. Not sure how to fix it.
Iâm wondering if your $30 & $31 values are correct.
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