Those heather greys/charcoals scorch like crazy, we've started running them with an IR flash now. We usually found the scorch was in areas not glued down to the platen. I guess the platen acts as a heat-sink when the shirt is adhered to it. I'm not sure how that relates to the problem you see on those shirts as you'd think the area you saw scorch on is where they'd be glued down. We shorten flash time and raise the flashes when we have to use quartz flashes on those colors of shirts, and make sure our pace is steady and doesn't speed up, sometimes speeding up like during a print finish cycle is enough to start scorching.