I personally actually only use my pointer finger underneath the disc. The pad of my pointer finger is rested on the inside of the rim. My middle finger is actually on the outside of the rim and my thumb is placed on top. If your going to use the middle finger as the finger your releasing from make sure the pad of your finger is on the inside of the rim. This is where you will obtain your torque from. Biggest thing is though use what is comfortable and consistent for what works with you.
PDGA Number: #58513
"Go all out or don't go out at all."