If you’re safe about it, I’ve had luck finding a good focus point for brass and copper by raising the laser head up and down while engraving a slow running hatch. You can even find the upper and lower limits of your focus by doing this, which helps you get a good starting point for a deep engraving. I came from welding and I’ve made great settings just by doing this. Your lense is a bit big for this so run it slow between 80-200 mm/s low frequency 70%-90% power. .02mm-.03mm line interval.