As for the hot spot in the lower section, I note that the flash head actually points slightly towards the inner face of the diffuser, and that will contribute to this effect; perhaps a business card or even a small piece of reflective aluminium placed in the flash head a la press photographers, might be the answer.
Yep you are right and what I've done to help is to extend the built-in bounce card on my 580EX before inserting it into the ring-flash and that helps a lot. So for the next round or starting a new one, I would try to make it insert as straight up as possible.
Welcome to the forum and thanks for posting...please do post your progress.