Yes I was waiting to see if GF already does some defocusing at low LPI but you indicate that it doesn’t.
There is a limit to how wide you can make the beam simply by lying about the material thickness because you only have ~ 0.5" minus your sheet thickness of focal range to play with. And very wide beams have much less power density, so you would need big changes to power and speed to compensate. So some of the very low LPIs are out.
So how about trying 75LPI which gives an additional height of 0.19". That is quite extreme and gives a spot size 11 times the area of the normal one, so you would need to increase the power / speed ratio by 11 to get the same depth.
The easiest material to test it with would be 3mm acrylic I think. With wood you get ridges due to the grain.
Once you get to 270 LPI the focused beam is already more than twice the line spacing, so I would expect lines not to be visible. I that the case? If so defocusing is only needed and practical for 75, 125, 195 and 225.
Tests of a simple circle raster engraved in thin acrylic at those resolutions with and without defocusing would be interesting but I would test the hypothesis that lines disappear at 270LPI with no defocusing first. If they don’t then I would go up in LPI at normal focus to see how much overlap gives a flat result.