Hello,
If I understand correctly, you are allowed to exceed the number by up to max. 0.8 for a carport/garage.
This cannot be answered like that, as the development plan or the textual provisions of the development plan are decisive for this. Every city/municipality has the right to alter/extend the applicable state building code with its own points, and these then apply "before" the state building code.
If you want to know exactly what you are allowed to do and what not, look at the development plan or ask the building planning office responsible for you.
Rhineland regards