KB107 (0.30) Pistons undersized?

I just got a call from my machinist who was cleaning up my 360 block for rebuild. He found that the brand new KB107 pistons I bought from Summit were actually 0.002" undersized, giving a clearance of about 0.004" in the hole. Apparently, according to a race builder he called to ask about it, some high(er) performance pistons are machined slightly smaller to allow for more heat expansion in racing?

Anyone ever heard of this/had problems with this? I saw nothing on Summit or Jegs to suggest a 4.028" bore for these pistons!

Also, is 0.004" piston clearance a deal-breaker? My machinist suggested that it could wear the rings out much faster in a daily driver...

Thank you for your thoughts.