Basic in Topological Associated Domains

Hi everyone

I am kind new in this field, I am trying understanding 3D architecture organization in human genome. I have some basic questions about bin sizes. I did not understand so well. I know this is the resolution of data and low bin sizes means high resolution. So, bin sizes could be interpreted as coverage with this I want to say the length of TADs fragments ?

I saw 3D genome data in this link (3dgenome.fsm.northwestern.edu/publications.html), It has bed files from human genome that contain TAD regions. I understood that almost all of them are in 40 kb except some files. However with my poor interpretation of bin size, some files that I understood to have 40 kb for all TADs regions do not have.

Thanks in advance