Been cutting a heap of black 3mm acylic lately and these settings give perfect results every time with every piece falling out completely.
This is CAST acylic (to test I burnt a piece and as far as I know cast-crackles and extruded-drips flaming melting plastic)
Also found that it is hard to engrave cast acrylic but these setting although slow, work well to give a light etched look (the faster speeds gave more artefacts in the etch)
faster but not as clean an engrave/fill
once these are assembled they are bases for aquacultured coral to grow on, pretty happy with the results