Hi, I almost started tacking up my firebox when I realized something. I haven't cut my FB to CC opening all the way up. I did it with cnc plasma beforehand, so there's a rim of around 2/3" on top. Here's a Sketchup model how I cut it: Will this be a problem? I know some hor air could get trapped in there, but surely less than an inch wouldn't matter right? My design is similar to Ribwizzard's, main intake is on the bottom of FB and there's also a second higher intake on the door. I can still cut it all the way up before welding, however I'm concerned about the strength of the box if I cut it beforehand. Cutting it afterwards would be hard, since I don't own plasma.