Cc'ing a head tools?

Not sure I am understanding this.....
"Calculate the volume of the cylinder as if it were a flattop with no reliefs, then cc your cylinder as if it were a cyl head, and compare volumes."

My H655CP pistons are below the deck. So I would drop them in cylinder to x depth, fill with fluid, measure and calculate volume. Does it matter that my pistons are dished? How does that factor?
Piston Head Volume (cc):
+11.23cc

View attachment 1715769144


Anything below the deck at TDC adds to your chamber vol wrt calculating the c/r