Admin not discovering my custom flex-object directory type in plugin folder

Hello, I'm trying to create a custom directory type and I would like to contain it, together with other related features, in a plugin. The problem is that the flex-objects plugin doesn't recognize when I add [my-custom-data-type].yaml to user/plugin/[my-plugin]/blueprints/flex-objects/, however, it does recognize it if I put the YAML file in user/blueprints/flex-objects/. What could I be missing to be able to make a flex-object directory type from a plugin?