ImperialFighter said:

Monroville, although I quite liked darth_ender's possible explanation HERE of how Luke managed to be 'sucked into' the side from the middle of the wide chasm, your theory of Vader using the 'Force' to steer him over is interesting too.

But I've finally settled on this alternative notion now -

Since Luke has had some 'Force' training by this point, I guess he might have been able to 'influence' his trajectory mid-fall towards the 'vents' himself ..

It's not a big deal, as it's more a "using your own imagination to explain a little thing". I felt Vader was possibly giving him a push, as it was his son and he wanted him alive. Luke, on the other hand, was committing suicide... so regardless of him having the power to push himself to one of the vents, I don't think he would have done it, as the whole point of allowing himself to fall was to keep himself from Vader and the Emperor (think of the music John Williams used when Luke takes the plunge, and how Luke was NOT screaming when falling. People tend to AHHHHH! when they fall when it's unintentional. Luke intended to fall [to his death], so no AHHHH!).

Regardless, whatever makes one comfortable with the scene is all that matters.. you know... as opposed to refilming the entire shot with a stunt double.