I'm insulating hot water heating pipes (black iron pipe) in my basement using 1"-thick-wall jacketed fiberglass tubes. At one point one of the pipes passes right under a 2 foot wide A/C duct. The tube won't fit at the top of the pipe since it's too close to the duct. What's the best way to insulate that section? Do a relief cut that's so deep that there's almost no insulation left at the top, but still retaining the jacket (which would probably deform due to almost no insulation left)? Or cut out a inch or two wide, two foot long section at the top of the pipe? Or ... ? Moving the heating pipe, or moving the A/C duct, is NOT an option. Thanks.