No, I had not seen this article. It certainly is comprehensive and represents a great deal of work.Here is a link to a substrate analysis that was shared from another forum. I am not sure if Diana has seen this one or not. I would be interested in her comments about it.
I believe you concluded that you got good plant growth from several different substrates. That has been my experience.
Two quick comments. You've described several substrates that will cloud the water. I'm not sure I would discount a substrate on that basis. When filling the tank for the first time, I often get cloudy water. The trick is to drain off the cloudy water and then refill the tank until you get clear water. When setting up my 50 gal, I had to drain off water 3 times with Home Depot's generic "Top Soil". But 6 months later this tank is doing great and the water is always crystal clear.
Then, you advise that hobbyists terrace tanks to a substrate depth of 6 inches in the back and then 3 inches in the front. In contrast, I recommend that hobbyists use 1 inch of soil covered with 1 inch of sand and/or gravel. I get good plant growth with this recipe, and any temporary problems (algae and/or fish distress) are manageable.
If you are truly recommending 3 to 6 inches of substrate, I think you need to qualify exactly what substrate you used and then show your results. In my opinion, a soil-based substrate of this depth could cause major problems for many hobbyists-- not to mention the fish.