I’m not sure what you are expecting. I’m not familiar with your model, but heat typically isn’t vented into the cabover area because most people want the cabover area to be the coldest part of the TC. There are a few fixes.
1. Insulate the cabover area. In my case, I used Reflectix under the matress in the cabinets, and in the windows and skylight for night.
2. Add a small fan like a 12V computer fan that directs heat from below into the cabover area.
There is a lot of emphasis on putting at least some warm air into the basement to ensure pipes don’t freeze. I think that’s what you are upset about, but I think it’s a lack of your understanding. I could be wrong of course.
