Questions for Harley Physicists and parts Experts.

Couple questions.
1: How does a does a Big Sucker, Fuel Moto, SE, or K&N intake increase the intake air flow when the butterfly diameter has changed none.
a: my answer would be the butterfly is capable of more cfm with less restriction
upstream. Is this correct?

b: Will a Big Sucker make any difference with a stock cover as compared to a
K&N filter only under a stock cover?

2: How come they always list Stage 1 intake parts up to 2014 for Touring but don't
include 2015. Is their a difference?

3: Who makes a good airbox if the stuff that fits under a stock cover is a waste of
money?

4: Heard from what I would consider a fairly credible source that there are a pair of
small catalytic converters in the stock mufflers in addition to the converter in the 1
section of the 2-1-2 stock header. Is this true?