Isn’t the stuff only about ½” thick to begin with? Yes you’ll loose more heat though the grooves, but isn’t that akin to saying you’ll get colder outside during winter in a tank top than in a tee shirt? If you don’t start with much insulation to begin with, I’m not sure it’s worth worrying about those grooves.
The insulation value in something really comes down to how many little pockets of air there in the material. Natural wood has a lot of little pockets and tunnels for air to get trapped and act as an insulator. However wood is typically only good for about R1 per 1” of wood!
Compressed wood like T111 is going to have much worse insulation value than even real wood I would think (Don’t know the numbers on T111) since there is going to be far less places for little bubbles of insulating air.
The best insulation (sans a true vacuum and areogel) is foam which consists of millions of little bubbles of air (or other gases) which retard the flow of heat/cold from one side to the other. If you don’t want to lose a bunch of heat through the grooves of T111, wrap the whole thing with foam. Polystyrene or Polyurethane.