I do think results can depend on the glass. The problem is the laser doesn’t really burn away the glass, it chips out little tiny pieces and in some glass it makes for the really rough appearance you got. I haven’t tried it, but my guess (emphasis on guess) would be that defocusing the laser a bit might help along with a high LPI setting.
Here’s some of the glass discussions I remember and there might be some setting in there to help you out.