Need help with laser cutting acrylic

[mondrota]

Hi all and thank you for taking the time to read and hopefully respond :)

So, I've got a Chinese 100w co2 laser (although I'm now suspecting it to be an 80W marked as 100W). I'm using it to cut parts out of 10mm cast acrylic. I know extruded cuts better but I can't find it in black in 10mm thickness. Anyway, I've had to align mirrors, etc to get a decent cut, however, it's inconsistent. It seems like the edges melt instead of cutting cleanly in some places, the other areas cut ok. I've noticed it does this mostly at the top of the cutting bed so I began placing the acrylic sheet lower down and the cut was better, however, I then made a trial cut at the top of the bed again and the cut was good. I've double-checked the mirror alignment, the beam enters the head in the same spot, regardless of the head's position. The bed is also level in relation to the head. Please see the attached pic. (I was having trouble adding more photos). I've also just ordered an ammeter so I can monitor the power as it cuts. Any ideas or suggestions would be very much appreciated!

Thank you!