I almost didn't link the entire conversation, simply because I only wanted the chart showing relative amounts of surface area of the various media. I must say that my take on this is quite different than yours; the writer states clearly that he was wrong the first time he presented his analysis of the info, and frankly I think he is still far off the mark.
Do you really believe that holding up the medium and trying to see through it is any kind of measure of effectiveness?
He is suggesting the same nonsense that was used to market the earliest canister filters many decades ago, i.e. you can go many months between cleanings, and the longer you can "get away with", the better. Honestly, this guy sounds like Father Fish; that's a bad thing.
The notion of increasing the contact time of water with the medium is an old idea, and...as long as it isn't carried to extremes that are unlikely to be achieved in the aquarium...still has merit. The writer is suggesting that wooshing the water through the medium at the maximum possible speed is beneficial; again, perhaps true up to a point, but extremes must be avoided.
If you have a pump that moves 1000l/hr, moving your water through a sheet of foam that is 1 foot square, you will filter you water nicely. If you then double the area (not total surface area, just the area of the mechanical filtration chamber, you will then halve the speed at which that same volume of water passes through the medium, since it has twice as much space. All other things being equal...biomass in the tanks, etc...nothing will change in terms of biological filtration. There won't be more bacteria, since there is no more food for them, but they will be more thinly spread over the larger area.
He talks about the speed at which the medium clogs, and this will happen much more slowly in the second example...but the whole idea of biofiltration is for the medium to
never be clogged; it's the mechanical filtration medium which is supposed to remove solids, preventing them from ever getting into the biomedium in the first place. In practice, this is never 100% effective. You will occasionally need to rinse the accumulated fine material from the biomedia to keep it free-flowing, but that should be a rare thing; it's the mechanical medium which should be cleaned...and frequently, not just once a year!
This started out as a discussion of Aquaclear HOB's. IMHO, the best thing to do is simply place 2 or maybe 3 layers of foam and call it quits. Whatever extra surface area you might get from a tiny spoonful of ceramic rings isn't worth even mentioning. And you are probably best off to forget about separating biofiltration and mechanical filtration into two separate categories in that tiny few square inches of space. Clean the bottom sheet of foam (i.e. the dirtier one) weekly in tank water, then put it on top of the other sheet. Doing that every week will allow both sheets to function as both mech and bio filters, and you will be alternately cleaning them and reversing their locations in the filter.
This isn't just theory, that will be re-thunk and re-explained next week and then reversed again the week after. I did it this way in multiple tanks for many years. It works great...until you eventually realize how much better and more convenient a sump is...