That's the weird part - they're not prevalent on either the center or the outside. Imagine taking a roll of 1-1/2" masking tape and wrapping it around the tire evenly spaced about 1-1/2" apart - that's what it looks like.
When first wiped them off and looked, I saw a the rough on the edge of the tire, that stopped an inch or so in. I thought - oops - a bit too soft. Then I looked closer, and there is another strip of rough a ways inside that, then a smooth strip, then a rough strip...