matched inlets question?

[Setone]

Been looking at getting a pair of matched inlets, question is when the inlets are getting matched ie to the head / to each other. Is it only the part in which they meet or is the whole length of the opening that is worked?

Also I have a ph1, will any inlet from the 1*2 range fit?

 

[Fred@BTM]

head to manifold
manifold to plenum