I have 6.3 m in the bungalow.
Oh, they must have sold you a commercial hall as a bungalow
Show some pictures!
...from when is it still considered a knee wall and from when is it a full storey?
I think the OP is not concerned with the legal term "full storey," which no longer exists in Bavaria anyway, but only with where the roof starts: below or above the 2nd floor ceiling. I consider the latter to be more advantageous. Ultimately, however, the shell builder should know best. He can compare the alternatives, then you can see where the money goes.