if you go to
http://www.rulesofbaseball.com (the J/R manual web page), you should check out their sample e-book. It covers this DBT stuff.
But yes, you and Pete pretty much have the idea.
FED: Only need one part of your body touching LBT ground to be considered in LBT (this goes for standing and lying on the ground). Once your whole body or 2 feet are in DBT, you are in DBT.
OBR: Need 2 feet on LBT to complete the catch. You then can carry the ball into DBT, but need to stay on your feet to keep the ball alive. If you are on the ground- as long as more than half of your body is on LBT, you are considered in LBT.
In both cases the line is considered to be part of LBT.
Sorry, i don't work NCAA to give you the interpretation for them.