How to keep grey band from growing too quickly during sear (under 75 seconds)?

I've been having an issue with my reverse sear process. It usually takes around 75 seconds to develop a really nice, conplete sear on my steak in a cast iron pan, but by then the grey band gets pretty thick, like 1.5-2 cm.I see people sear with higher temp methods like charcoal chimneys for longer times, but don't get a grey band. Is there something I'm doing wrong? via /r/steak https://ift.tt/2HusAYM