I would use the plugin when it will be possible to configure case part case, the it's line part line it does not suit me I need case part case can you make it configurable?

What does that mean exactly , slot by slot ?

This has been suggested before. I might implement it in the future but the performance cost of checking potentially 42 different permissions (some people want that many different sizes) to see how many slots you should have would be a bit ridiculous, so it will likely need some optimization work.

https://umod.org/community/backpacks/30256-assign-spaces-instead-of-using-row