ketchup, I can appreciate your logic concerning the mat you have and I agree on a hard mat that makes sense as the only way to go. However I have a felt mat on my Rega and would think that the vinyl rests with a fair distribution of pressure across the playing surface. In addition to that I have recently added a Michell clamp to my TT and hope add to that equalization of pressure. I do realize that the raised edge and lable area have been on records for as many years as I can recall, of course that practice goes back to the days of stacking records on automatic turntables. A practice that hasn't been used for decades, so it kind of suprises me that modern day records are still pressed in this manner. But I guess it does drastically reduce the chance of the stylus exiting the record off the lead in.
But again at the end of the day, I appreciate the time and effort you spent pointing out the variance in thickness. I found it mind provoking in the physics that a tonearm and cartridge must overcome in revealing the information found in these "somewhat" flat peices of vinyl.