backflip 540: 1.5 full (Rudy)
Frontflip 540: front 1.5 full (Front Rudy)
These are aerials maneuvers; straight backwards/front, completely upside down.
misty, on the other hand, is almost like you are rolling on your back over something (rolling over a table...), so you never go completely upside down. it is misty 5 because you spin a 540, not 360 flip plus 180 spin (which would be a branny[front 180] or a flare [backflip 180]).
rodeo is a similar concept, like you are rolling over something behind you.