ragged claws - welcome to the Forum. As you've guessed by now there is no "hard & fast" way to determine which CG has the roomiest sites. I do agree with the reply to your post stating older CG's tend to have smaller sites. Compared to today, motorhomes and TT's were relatively rare; most of us in the mid-60's and early 70's were in pop-ups and tent trailers so parks dating from this time are going to be cramped. As to difference between private CG's and state parks/COE, etc. we've found cramped and roomy sites at both.
Sometimes "elbow room" can be a relative thing - we've been in a number of CG's what have lots of trees and shrubs between you and your neighbor and that is usually sufficient privacy for us.
It often is a matter of trial and error so keep track of the CG's you like. Good luck and safe travels.