Questions about Innate Attack (Wall)

[Varyon]

EDIT: Note this thread has been raised from the grave by necromancy most foul. New posts start at #9.
EDIT2: Even fouler necromancy has raised this thread yet again; new posts start at #37.

Alright, so the recent Wall thread is making me wonder quite a few things about the Enhancement that I'm hoping to get clarified. Note for the following questions I'm referring to "Innate Attack with the Wall Enhancement" as simply "Wall."

First, height. Do Walls follow the general GURPS trend of having each hex be essentially a 1 yard wide by 4 yard tall hexagonal prism? If not, how tall are they meant to be? Can we reorient them to lay on their sides, or particularly with the +60% version thin them out to get more surface area out of them (while maintaining the volume)? And why are hexes 4 yards tall to start with?

Next, shells. How exactly should one go about using Wall to build a shell - that is, a wall with a roof? The way I handle it, you need full sized walls for a base, then more on top, and then you can fill in the empty space on the second level to make the roof. Is this correct? Note this requires 13 hexes to build a shell over a 1 hex "room." On that topic, how do you have a Wall that can manifest underground, so that foes can't simply dig their way into or out of a shell?

Another question would be climbing. When a Wall is defined as being rigid, how difficult should it be to climb it? Would it be appropriate for such Walls built from Cutting/Impaling attacks to risk cutting the character as they climb? And how would we adjust difficulty, if there's one character who makes walls of rough stone and another who makes them of mirror-polished metal?

Yet another for rigid walls would be weight. Should walls be considered as having a weight, and if so, how much? Is this a case where we should simply back-calculate from HP, assuming a homogenous target? PK had a great suggestion here for determining how much weight a Wall can support, but it also seems like a terribly strong foe might be able to pick up and throw a Wall aside, rather than smashing through it, so a weight for the actual Wall might be appropriate.

And how about hybrid walls - say, a wall of crushing force that deals damage to those who try to pass through it and requires them to physically break through? I think the RAW would be to build two different Wall abilities and Link them together, but would it be legal to have them exist in the same hexes?

Related to that, how about transparency? Is transparency/opacity a Feature? What about a Wall that is, say, opaque to visual light, but transparent to IR?

EDIT: From the other thread, do walls - be they permeable or rigid - require contact with the ground, or could they be made to simply hover in the air until they expired or were destroyed?

And one I had initially forgotten about - do walls have a minimum thickness, and if not, when making them thinner than 1 yard, can we use that volume elsewhere or is this a case where you are basically just condensing the wall down? If we can use it elsewhere, would it be appropriate to scale damage/DR+HP linearly with thickness?

I'll probably think of more later (I thought I had others earlier, but can't remember them now), but some answers on what I have above would be greatly appreciated.