Antichton, I appreciate the well thought out response and the link –
From what I have read in the past and reading the info you provided along with the info in this link, https://www.2hraquarist.com/blogs/choosing-co2-why/how-to-push-the-limits-of-co2-safely it seems to me the larger the bubble (and fewer of them for the same volume of air), the less efficient in creating surface agitation (for gas exchange). For my purposes this is a good thing.
I’m going to assume running a sponge filter (at my typical rate) without an air stone produces a bubble that is about ½ inch in diameter when its breaks the surface (due to the pancake shape). The surface area of each bubble would be about 0.2 sq in. I would estimate there’s only room for about 5 bubbles per inch of height.
Using your example of a 20 high, the bubble surface area would be 0.2 (sq in.) x 5 (# of bubbles per inch) x 16 (height of the tank) = 16 sq in. which increases surface area by about 6%.
This falls well into my acceptance of how much the CO2 loss increase would be using sponge filters vs a canister.
Hopefully, there’s enough errors in here to cancel each other out producing a somewhat accurate result!