Someone on the dnd forums actually posted something about this and it really, really helped me. Now i can get the change 100% of the time and 90% of the time it lands perfectly.
Dan and Dave never actually learned this move from a proper source ( from what i've read,.. ) . They teach it 50% correct, your fingers are in that position, but you do not angle it 45 degrees. Grab a 7 of hearts, when you do the move your index finger should rest right on top of the right curve on the middle heart. This moves the card pivot and flip.