In the file chooser dialog, after files are selected, click the [+] button rather than [Import] button, all the files will be added to the list without copying. Reasily reads them from the storage directly.
This is useful if you manage your epub files by yourself in your own storage folders.
Note: If you [Import] books into Reasily, the files will be copied into private storage of Reasily app, and the size you see in the application info will grow. After books imported, you can remove them from your download folder.