Torch Height Control Malfunction

I'm new to CNC plasma and continue to have issues with cutting with THC enabled. I have a Shop Sabre with Hypertherm 45 XP. When cutting longer contours the torch will lift after about 8" of run and essentially gouge the metal. Example, say I'm cutting a 18' x 24" rectangle with an internal image of a star with lettering, all the letters and star will cut fine but as the torch moves to cut the perimeter it'll cut 8" +/- just fine and the torch will rise and gouge. I've done test runs of just lines with the THC disabled to see what the voltage is doing through the run, then set voltage in the config screen about 5 points less than the highest voltage in the cut. This helps but I still waste 30-40% of my metal trying to get one decent, complete cut. I'm concerned I have an issue with the setup, torch or the winncnc software that causes the issue. If I run the cuts in THC disabled its pretty good but on thinner material where warping occurs it will often drag the tip and knock the torch out of plumb. HELP. Appreciate any suggestions.