VAT coefficient is calculated using a uniform method, according to Gazeta Prawna

The VAT coefficient is calculated using a uniform method.
The municipality cannot choose its own key for calculating the deduction ratio.
The calculation method should correspond to the specific nature of the taxpayer’s business.
The VAT law does not specify a specific method, but provides examples of data that can be used.
Examples of data include the average number of people working solely in business activities and the average area used for business activities.

Note that this post was (partially) written with the help of AI. It is always useful to review the original source material, and where needed to obtain (local) advice from a specialist.