How to set the -dim values(sample area) for genBSDF?

I was reading the BSDF tutorial( In the first example in this file, which illustrates how to generate a BSDF XML file for Venetian blinds, it looks like this XML file is generated just for one slat, not the whole Venetian blind. I am a bit confused, why doesn’t it use the actual geometry of the blind to generate BSDF? or does that means the actual sample area does not matter as long as it is representative of the system as a whole?

Any help will be really appreciated

I have just modified the sampled area and generated two different XML files. The comparison between these two derived matrices are shown below.(Direction is transmission back)

Clearly, they are not 100% equal while really close. So I wonder if this means the dimensions of the sampled area do not matter and this difference is acceptable.
Screenshot 2021-02-26 002046