Rob,
As Miller has stated, a tube of a given wallthickness is able to sustain higher pressure if it is of smaller diameter. However, in practical terms, the .008" diameter changes are so small of an impact to a 12g tube that it is likely less than pressure variations shell to shell.
As for a flaw on the inside or outside of a tube, the outer surface sees higher stress than the inside. You decide whether additional damage from residues is likely to be of concern. On a blackpowder gun it would definitely be a concern. Smokeless stuff with non-corrosive primers? I'm not convinced since I have several guns that have had stable pits for years.
