It's easier to figure out something is wrong when using a flat top piston.
When you do the down fill you can easily calculate the valve notch volume doing that, and almost all the time they are bigger than advertised.
It a bit more difficult with a domed piston. But you can do it. It's also quite funny that dome volumes are usually not what the piston manufacturers claim. They are usually LESS that advertised.
That's why I don't like taking the word of the guy making the Pistons. They are wrong often.