It’s not very clear to me what you are referring to. I assume you are referring to individual files having the ability to have a higher price than the project itself. If that’s not the case let me know.
Developers have the option to set a higher price on individual files. These prices function as a “Tier”. So if you’ve invested for example $10 on a project, you will have access to every file with a price of $10 or below. This is something each developer has as an option, how that is used is up to them.
If you don’t understand what the file adds to a project, you should probably post on the game’s page, or otherwise contact the developer, as they would know all the details.