Okay, so I've been practicing the rear palm lately, but I've been having some issues. Couple questions:
Is a rear palmed card supposed to warp a bit, or does it lie completely flat on the palm of the hand?
The palm is no way the easiest. Also, keep in mind that having very dry hands will make relying on this palm impossible, and your study will mostly be academic.
To help a bit, for a start, think of it as the CORNERS of the card is held between the 2 fingers mentioned in the book.
You could hold the card flat if you have some very sweaty palms, but its not needed, the card held will look exactly as the illustration in the book.
The card will be wrapped, the more moisture in your hand, and the longer the card stays palmed, the more wrapping you'll get ( e.g. handing the deck to be shuffled ), but its still nothing you can't fix, especially if you're doing a card to pocket ( fix it in your pocket and as you take it out by bending it the other side ). If you want to replace it on the deck, replace as you bend the deck lengthwise.
There are very few magicians to my knowledge who use the rear palm in their work. I had the pleasure of talking to one who uses it extensively, it certainly worth it if you take the time to learn it well.
Most Magicians use it for color changes, since the card is held for no longer than a second or two.
edit: oh yeah, the angle assuming card is held in the right hand: If you hold the card towards your chest ( the side of your hand will be towards the floor ) and slightly curling your fingers ( so only empty windows are seen ), then you'll pull it off with 180 safe angle. Other than that, always be careful of your direct left.
Hope this helps,