I just use an old soldering iron that I have. That way you seal the fibers together and it's a much cleaner look without worrying about unraveling on loop carpet, Cut pile doesn't make much difference, except it does make a nicer hole. I do 60's Lincoln Continental heel pads on sewn carpets and we sew them onto the carpet. The measurement is general since the cars are all different.
Put your foot on the gas pedal and mark where your heel hits. you want to be 1" or more inside the heel pad.
but generally 1" to 3" after the curve of the firewall to floor. closer to 1" is better for your heel that is resting on the gas pedal and pad here is a parchment and an off white one we made and they are going on a sewn up carpet set this week that's going to Finland.
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