Engine milling maths

For 30 years I’ve been milling the intake surfaces on heads the corresponding amount that goes along with how much the decks have been cut.
I’ll probably just keep doing it that way.

Does that mean an intake manifold doesn’t ever need cutting?
Not by a long shot.

But what it does is reestablish the relationship between the port height and the mounting width back to “normal”.

If you have a set of heads and intake manifold sitting on the engine, and the intake fit is good....... you can mill the decks and intake surfaces, and everything will still fit like it did before the heads were milled.