Yes, it actually works better if buried. That’s when the root demand action kicks in. The root exudates pull on the water supply when the plant needs water, stops pulling when they have enough. Also being buried prevents UV from making the tubing crack and split. If buried, it can last over 25 years. Burying it also lets you plough or rototill over it in the spring. Don’t bury more than about 8’’ deep unless only covered with mulch, not soil. If installing under athletic grass, make sure it’s at least 4” under to prevent sogginess.
Often water supplies have large amounts of dissolved gases and we don’t want that inside the Blumat cones when setting them up. For soaking and initial set up, it’s best to use clean rainwater or something similar. You can also boil water to dissipate the gases, let cool, and then use that to soak the carrots.
In a plastic pot, in doesn’t make as much difference but in a fabric pot; it’s important to not place the carrot too close to the side. Fabric pot sides dry out more quickly and if the carrot is too close, the water inside it could be pulled out leading to slower on-off cycles or even run-aways.