Thanks for all the comments.
Yes, the substrate is too deep. I was unprepared for how light and fluffy Turface MVP is. I bought four bags and used three. Two would have been sufficient. As a result, and in my haste, I ended up burying the return strainers. I had to dig them out and cover them with rip-rap to keep the substrate from smothering them. If it works, I like the look. I don't know if I will eventually have to raise the strainers higher.
No real defensible reason why the old substrate ended up on the bottom. The 55 had been setup for years so the store-bought nutrients in the EcoComplete were long gone. I wanted the old substrate in the tank as a bacteria source, and I thought that having some fine material on the bottom would encourage de-nitrification. (I am not afraid of aneorobic activity in my substrate. In fact, I like it. It is natural.)
The playsand is on the top because I like cories and may eventually have a school of them and the soft sand is good for their barbels. However, the turface, being so light, is already making it's way to the top so that may be a losing battle.