We determine the focal point size by the width of the line it burns. The .005" is in inches which would be .127mm. It's not easy to measure, other then setting the Pixel Resolution (stepover) in our software when generating the gcode. Then run an image engraving test to see if there are spaces between the burn lines with an eye loop or magnifying glass. If the burn lines are overlapping, then you use a larger Pixel Resolution value. Engraving at a 45 degree angle will bring the burn lines slightly closer together.
With a .005" burn line width, we use a .006" Pixel Resolution and engrave at a 45 degree angle. This will cut down on the gcode's travel perimeter distance to cut down on the overall run time.