Inconsistent burn


Noob, six months in here. So I’m having an issue where I’m getting splotchiness after I wash the piece. I’m using the Norton tile method and all of the tutorials I’ve seen they say to use two coats of paint, which is what is displayed in the attached picture.

I have had success with using three coats but my interest in two is to be able to cut down on my burn time as well as the amount of paint used. I am open to the possibility that I may spray the coats on to thin. My method of spraying each coat is girst cleaning the files with acetone. Then ,starting at the bottom I spray back and forth with a little overlap, then rotating the tile 90° and repeating. I am burning gradient test tiles which are consistent with each other. I have also tried burning the same file on my brother’s K-40 with similar results, however I cannot remember the settings I used on his

Technical info: Ortur LM2 20w (non-pro) using lightburn
Speed and power: 750mm/min @ 90% for the failure, 500mm/min @ 100% for the sucess.
All files are vector graphics .svg files, designed in inkscape.

Also, please excuse the chipped tile. I dropped it while washing. (Oops)

Thank you in advance for any advice and tips. If more info is needed please ask.