I never saw the vane as directly part of the carbon chamber.

I thought the vane and the rooms inside were part of a power plant of some kind (possibly using the up and/or down draught from the pit as a power source). The tendency of Lucas to recycle ideas and virtually the same concept turning up in TPM would seem to back up this personal theory. I imagine all of these concepts would have begun as bits of the Death Star when he was daydreaming The Star Wars into existence.

So while it made sense to put a power hungry process like the freezing chamber in an industrial zone near the power station they would be seperate areas in terms of functionality.

The area where Vader chucks stuff (technical term) at Luke seems to be full of control consoles and power readouts rather than anything directly associated with the freezing chamber which has a very different character.

I liked the extra vanes in McQuarrie's pre-production paintings but I can see why they removed them.

If they were as close as they seemed to be in the paintings Luke could have just jumped over to one of the other ones with his new Force skills rather than dropping down (anyone who's played Jedi Outcast would be used to this maneuver and the tedium of getting it wrong).

I suppose if the vanes were shown to be significantly far apart so that even a Jedi couldn't jump it (something which seems almost impossible to imagine the PT Jedi having a problem with) it would be nice to see them if they didn't get in the way of the scene.