Ok, having Sn in the RS274NGC_STARTUP_CODE in the ini file works.
On your plasma do you use different nozzles? I'm working on a plasma configuration that allows you to pick the nozzle then the material thickness and the cut height, pierce height, pierce delay and cut speed is inserted into the touch off subroutine. As well as the amp and volt settings for the torch and THC. I was trying to insert the info into the writeHeader function but it is not available at that point.
Are you offsetting your dxf profile by 1/2 the the kerf width? How are you handling the lead in and lead out on your parts?