nahh, the box doesnt need to be super long, i guess its better though because you get more time to orient yourself on the box.
but really just get on the box with the mindset of doing a switchup, and then pop off like 6inches from the end of the box , starting your rotation. by the time you hit the ground you should be landing straight and cleannnn.
also idk i might be just wierd but i didnt even think about sliding opposite when i first tried a 270 and it worked out fine, maybe im ambidextrous when it comes to sliding?