Being that I know my kerf is .007", I always just figure it in as I draw.
Being that your tube is 135 watts where mine is only 100 watts, yours will have a slightly larger kerf (more watts means larger beam. larger beam = larger kerf)). If you get and use the 2 1/2" GaAs focus lens, I can almost bet your kerf will be around .007" to .008"
Seams to me that there is a kerf offset in Lightburn somewhere but don't remember how to do it. It might of been RD Works that had it.