Nexus 7: Kindle app annoyances

I side load all my books, as I already have those on either pdf or txt format.
Here are a couple of annoyances, other than screen brightness I've already mentioned on a previous post, that I come across:

• Location/ directories

All the files have to go to the "kindle" directory.
There is no support for sub-directories; I'd like to keep my files nice & tidy, with an author/book tile structure.
This is not possible on the app, the files that are placed onto a subdirectory are simply ignored.

• TXT files

Unfortunately, the Kindle app don't read those. At all. Really sorry and strange.