Picked a very nice Mama Bear this weekend!

You will like that Mama so much better !
Sounds like you're referencing the clearance reduction table (12.6.2.1) with materials and specifications for wall protection correctly.
Duplicate of table 2 here; http://www.maine.gov/dps/fmo/documents/2005Woodburningguide_001.pdf

(e) states; 24 ga. with ventilated airspace allows a 66% clearance reduction. The table also was designed to prevent combustible surface temperature exceeding 90* f above ambient air temperature.
2013 is the current standard being used and 2016 is the next edition. Seems all the newer versions use the same specs, but put everything in sentence form leaving more for interpretation and a legal degree to understand.

As an example of what a little air space does, with your finger an inch away from a hot surface, you can go all the way down to about 1/8" without burning your finger. A quick touch burns, so that shows the insulating factor of the air space between your finger and hot surface. 1/8" being almost as good as 1 inch. Your cement board and tile works the same way transmitting heat in contact with the combustible surface behind it. If you stand a piece of cement board up close to a stove, the back feels just about as hot as the front facing the stove. That shows high conductivity, not to be confused with resistance. (R) It's all about the air carrying the heat away.

Baby just doesn't hold enough to be giving off good heat in the morning with a pile of coals to kick it right up. Mama will not only be going in the morning, but you should gain coals with 24/7 burns until you need to open it up and burn them down for loading room. Up here, too many coals glows all day, but doesn't put out enough heat so we need to burn it down. You may not need to burn that hard where you are, so every few days you can skip loading in the morning and let the pile heat the house all day until it's time to reload. I got away with 3PM loading after a few days of hard burns when the coals built up too much. Could never wait longer than 3 since we needed it for cooking supper before 5.
When we had the Mama as the only heat source, it was only the best oak we had nonstop. I would clean out the ash near the front where it burns down the best and rake the coal pile ahead to build the next fire on. Never needed to let it die to empty ash that way. For this winter, we would have needed a Papa in it's place for our 1800+ sq. ft. There's no interior doors in my place, and one small fan in a wall to equalize the heat. Open floor plan with chimney in the center of kitchen.
I built the place to heat easy, so that's the only reason a Mama could do it. The reasons for no longer using the Mama Bear is due to needing it in a log cabin for now, and I fell into a brand new Kitchen Queen I really wanted for a long time. At least 3 times the cook top, oven, water heating and a bypass for summer cooking without heating the 900 pounds of steel stove. Someone is also normally here to load it and keep it going very steady. My best investment was a simple $10 thermometer that holds 24 hour highs and lows. I find we get a little lax on warmer days and end up with a 68 low overnight and 75 high day. On colder days in the single digits and below at night, I end up with 75 low and 77 high. That's a very small span to maintain with a wood stove but that's what it repeatedly does when it's cold enough to make it really work. Really gets difficult when temps warm up above 50. That hasn't happened yet with teens at night, low 30's days. So next month we can only wait until the house cools down too much to start a fire and suffer when it gets too hot. That's when a Baby Bear comes in handy on another chimney for those shoulder season nights.