I use a Ortur laser master 3 frame and the laser module what I use is the Opt lasers XT50 45 micron spot and what I found out when I make engravings bigger then 200 mm the I can use 254 dpi and works great also on tiles for me and the laser time IIS also shorter.
Many of my work on tiles and the Tio2 mix I say before and I love working with it.
Mostly I use 254 dpi by a image bigger then 200mm in one side but smaller then I use 318 dpi but all these above are 254 dpi and just 1 hour laser time and very high quality.
All my images I prepared in DithX I made out and it is free if you like also to have free Acces just go to my dithx website and push in the right top to to Dithx then you see the button free registration and walk true the whole registration and I send in 24 hours always faster but you get your license code valid until 2050 unlimited access. dithx.optlasers.com
Have fun if you have questions always ask I happy to help where I can.