Neighborhood concerns regarding exemption from the floor area ratio

The federal government has passed a law, namely the Building Code (Baugesetzbuch), which authorizes municipalities to determine the structural and other usage of properties within their municipal area (§1 Baugesetzbuch). It also authorizes the responsible ministry to issue related legal ordinances, such as the Land-use Ordinance (Baunutzungsverordnung) (§9a Baugesetzbuch). To prevent, for example, the mayor of Monheim from coming up with the idea of allowing the complete construction over the entire municipal area in order to maximize trade tax revenues and stormwater fees, the Federal Ministry for the Environment, Nature Conservation, Building and Nuclear Safety devised §17 in the Land-use Ordinance. As the title "Upper limits for the determination of the extent of structural use" already indicates, this paragraph is addressed to the determiners, i.e., those who establish the development plans, such as municipalities or planning offices commissioned by them.

§17 does not concern the calculation of the actual plot ratio but only the determination in the development plan. A violation of §17 Land-use Ordinance only occurs if an error was made in determining the regulation, for example by incorrectly assigning an upper limit to a building area. If the municipality sets a plot ratio of 0.6 for a general residential area without sufficient justification, a lawsuit based on §17 Land-use Ordinance has very high chances of success.

For your neighbors, a plot ratio of 0.3 was set for a WA. This does not contradict §17. The regulation is unobjectionable. And if your neighbor plans to fully develop the property with an eight-story office building, there is still no violation of §17 since the determination of 0.3 remains legally valid.

The exemption from the regulation by the approval authority does not change the determination. It only allows the builder to exceed this determination. You can only take action against this permission if it violates your rights. And as long as the building body complies with the setback distances, I see no publicly protected neighborly interests affected by the exemption.

While you are being misled by the paragraph that does not protect neighbors, you forget to work on your arguments. You tirelessly quote the abstract wording of the legal texts. So far, the only concrete impairment mentioned was

corresponding shadow casting

about which I have already explained that the mentioned provisions do not apply. The statements

... impaired resulting from the large building mass ...
... consider the deviation ... inappropriate ...
... to protect the lower lying neighbors from overly dense construction ...
... like a "prison yard" ...
... with damage to us as lower lying residents expected ...

remain vague and would probably not offer any basis for any kind of lawsuit, even for an experienced lawyer.

Moreover one does not have to allow deviations according to §19

One does not have to cross a traffic light on green. Nor can you force a police officer to punish a red-light offender. Nor can you sue the police officer who allows a group of cyclists to cross at red while you have to wait at green and end up being late for an appointment.

While you are being misled by the paragraph that does not protect neighbors, you forget to work on your arguments.

Unfortunately, I have that feeling too. If you read through this thread again, it apparently only concerns the wording of the principle, but not the "subjectively mentioned prison yard." I also believe that exaggeration is a bad argument because it is unobjective.