When measuring actual down fill you cannot factor the deck height into the equation...

assume you have 4.00 bore, no valve pocket, no dish or dome for simplicity sake.

2x2x3.14=12.56x.500=6.28x16.387=102.9cc down fill.

we measure at .500 and get 110cc

110-102.9=7.1 cc extra vol. this mean/shows the piston is below deck .035 (2x2x3.14x.035=7.2cc)