That's why block decking to ensure HG seal was accounted for in the figures I supplied. Flatness, while a requirement, is only half the equation- the surface finish
is also important if using shim head gaskets. Coated shim gaskets are a little more forgiving but will still seal best w/the correct finish.
Had I also been discussing CR in that post (it was about quench, primarily), I would have said that milling the heads, while not affecting the quench, WILL slightly raise the CR. But I wasn't, so I didn't. Have to draw the line somewhere, lest the post turn into a freaking book. Like this one is fixing to do.