Ken Rajesky is quoted in a wiki link descdribing how stoves are tested for clearances
The benchmark temperature, which determines safe clearances, is typically 115 degrees F over the ambient room temperature. In other words, if the ambient room temperature is 70F, the benchmark wall temperature cannot exceed 185F. If temperatures exceed 185F, the stove must be located further away from the wall. That is why movable walls on tracks are used. If the temperatures exceed 185F, the walls are moved back until the temperatures recorded are less than 185F. In a nutshell, the stove is run through the complete test, the temperatures are recorded, and safe clearances are established.
Written by Ken Rajesky, Hearth Industry Expert. After the difficult decision of what stove to buy has been made, you’ll need to install the stove safely. However good the stove is, it’s still not safe unless installed to manufacturers specifications. First, review the owners guide that came...
Better to shoot for something a good amount lower and leave room for stove temps above the normal. The heat shield will do that. Yes, put up a proper shield and get that good night sleep. I was thinking cement board needed to be covered with tile but could well be wrong. If you would rather sheet steel a local shop should be able to cut you piece of maybe 22 ga and hem the edges pretty reasonably for that small area.
Funny thing, by the way, my new Etekcity infrared gun arrived and I used it for the first time today. It verified that my drywall temps were fine. Had the stove going good for a stretch tonight to keep the oven and pizza stone heating at 500. Wall temp still fine. Slick little device.