reynolds, the tape's put on the bottom of the recoil lug to allow clearance so the bottom of the receiver will clamp solidly to the bedding under it. If there was no clearance on the lug's bottom, it would not allow the epoxy to compress a tiny bit and allow full pressure contact all over its bottom. I use at least 1/32nd inch thick tape on the lug's bottom.
I don't put any tape on the sides or front of the recoil lug on my Win. 70 actions. Nor do I think it's needed on any other action type. Full contact with the bedding in those areas makes the receiver slide back into the same place each time it's pulled out of the bedding for cleaning.
I use Devcon Plastic Steel or MarineTex; these have the least amount of shrinkage when they harden. I've mixed a bit of baking flour with Devcon to make the mixture thicker and not run too much.
US Navy Distinguished Marksman Badge 153
Former US Navy & Palma Rifle Team Member
NRA High Power Master & Long Range High Master
NRA Smallbore Prone Master