KB243 Hyper Piston Confusion

Siksty7 Dart 270 said
Before I go inserting my foot in my mouth responding to a UEM Pistons representative, can someone tell me if I'm wrong here? I sent UEM an email asking if the compression height could be reduced by machining a KB243 piston shorter to achieve zero-deck clearance under a closed chamber cylinder head. Here's the response I received: "The deck of KB243.040 sits .012" below block deck @ TDC, on a stock LA/340 block. The .030" dome portion of the piston can safely be milled completely off , for use with a closed chamber head."

By my calculations 6.123(rod)+1.655(half stroke)+1.84(piston compression height)=9.618 assembly length. This is above the deck even with the UEM catalogs suggested OEM deck height of 9.599. Even the catalog indicates the piston is above the deck in that case. See screenshot attached.
My block before milling to flatten is 9.586". I was looking for a zero deck piston option for a street 340 without going to forged pistons.
Did the UEM rep look at a different piston, or am I thinking of this wrong?

View attachment 1716483397

The UEM rep is correct for the KB243's.

I have the same pistons in my 340, and spoke to UEM 15 years ago on the same topic. The top of the piston is .018" over the deck. But that's to the top of the dome! The dome itself is .030" tall, measured from the flat part or shoulder of the piston (above the ring lands). That puts the shoulder of the piston .012" below the deck. If the piston were perfectly flat, that's where it would be. Since it's not flat, the top of the dome is .018" over the deck.

I had contacted them about the compression ratio, because I was getting conflicting numbers. This was their response (15 years ago!)

"the protrusion has to be treated like it is a dome so the piston is down in the hole .012 and it has a .030 thousands high dome of 2.08cc's.This all equates to positive 7.3cc's.Use this to calculate your compression ratio"