Andy - I don't disagree. That data I referenced didn't include all the necessary background to fully understand (as I phrased it above) "... all of the other constraints (choke points, capacity limitations, etc.) for the test equipment used when comparing the same amount of filter area across different brands / types."

For example, what if all those tests were based on how much air someone could pull through a 1.56" v x 1.75" throttle race-type 4150 that might dry-flow 925 CFM at the same test pressure? Then it wouldn't be a test of the max flow capabilities for each 3" vs. 4" filter element, and, instead, how many CFM each filter reduced the carb's peak flow capabilities.

Assuming EVERY filter is going to result in at least some amount of restriction, then the smaller delta between the 3" and 4" versions of the same filter types might be explained because the 4" filters aren't being tested to their limits, whereas some of the 3" might be getting right up to their full flow capabilities.

Regardless, my intent was simply to add more data, unfortunately w/o being able to explain the whole test setup.