um kfw55 and kfw40, in addition to the system technology, output a maximum value for Ht' (transmission losses depending on the average U-value of the components) and for the primary energy demand per m2. Both in relation to a reference house according to the Energy Saving Ordinance: The kfw55 house is not allowed to consume more than 55% of the Energy Saving Ordinance house, and Ht' may, I believe, only be 70% of the reference house. (Kfw40 primary energy 40% and Ht' 55%)
Key point: The reference house has the same orientation, cubature, and window area. It therefore does not matter whether your house is cube-shaped or looks like the Great Wall of China; before the Energy Saving Ordinance and KfW, all are the same. If your energy consultant does not know this, then they also do not know what their software is doing. Simply increasing walls by one meter and seeing what happens does not sound competent to me. And to claim that it is due to the shape of the house is simply false. The Energy Saving Ordinance and KfW are neutral in this regard.
All of this can be found in the freely available Energy Saving Ordinance 2014/2016 Paragraph 3 (Building Balancing) and in the KFW 153 technical minimum requirements and additions in the KfW technical guidelines FAQ.