When treating tattoos its almost always necessary to use more than one laser. When they become resistant to one laser I believe turning it up by decreasing the spot size is more likely to cause a scar. Shrinking the spot size to increase the energy once a tattoo stops responding is in a way analogous to a bacterial infection that becomes resistant to a given antibiotic, one needs to switch the antibiotic (or in this case the laser) to a totally different machine. Tricking the spot size deposits the energy superficially which means that the laser energy is not treating the tattoo but instead is injuring the superficial skin of both the epidermis and superficial dermis and has a significant chance of making a scar.