Platter mat insanity

I was doing an idler upgrade to my 401 (more anon) and when finished used the Keystrobe disk to ensure speed. I use a 10" EP as a platter mat. I played a bunch of albums and it sounded fantastic. On the 6th side, I noticed I'd forgot to remove the 4" strobe disc. Duh. I took it off and figured VTA was responsible. So I lowered the arm to see if that made it sound so good. Nope. Put back on the 4" strobe disk and raised arm. The awesome sound returned. So air under the record removed haze, smearing, flattened soundstage and muddled bass; and made it so more musical. Comments...