This EXACT question was already posted on BGG, and answered there, but for the sake of redundancy:

There is no reason NOT to collapse down. Installing new ICE costs only as much as there is already ICE in the server. An 'empty' ICE slot costs nothing. [Edit: also, as ICE must always be installed in the outermost position, there is really no benefit to keeping an 'empty' space where there was ICE before.]

Rook counts position from the innermost ICE on a server (1 being the ICE right before the server, 2 being the ICE immediately outside that, and so on).

If you move Rook to another server, you move it to the same position, counting from innermost. This means that if Rook was the ICE closest to a server, it must move to the ICE closest on whichever server it moves to. It doesn't matter where on the table this ICE is positioned, but for the sake of clarity (and ease of play) the convention has always been to collapse down, even before Rook was announced.

Maybe he wasn't satisfied with the replies there, I dunno. Same guy.

Regardless: per the Core rulebook, p 13, the only thing that even defines ice's position is how many pieces of ice there are on the server. There's no such thing as which "row" it's in, that game concept does not exist.

Technically once an inner piece of ice is trashed, there isn't even a gap to collapse, the formerly 2nd piece of ice now IS the first piece of ice, and the formerly 3rd piece of Ice now just IS the 2nd, and so forth. Sliding the cardboard back into alignment with the adjacent servers is purely a courtesy. The wording is the same in the core rulebook and Rook, so there is no confusion at all.

You know, now that I think about it ICE destruction allows for some really interesting Caissa plays. Move your Rook somewhere it couldn't have gone before, or accelerate your pawns.

Thanks for the answers, The reason for the post here is in fact because I was not satisfied with the answers I recieved from BGG and I was hoping to get something more official here.

On page 13 of the rulebook, it talks about "the outermost position" being the position in which ICE must be installed in; Rules as written distinguish position and ICE as seperate things, not contingent like you suggest. I think you could be right that rules as intended define position based on ICE and not seperately, but that isn't how it's written.

However, it also says that ICE "cannot be moved or rearranged"; I don't think it would really be moving or rearranging if the definition of position depended solely on ICE, but that's not how it's written.

It also clarifies the order in which ICE is trashed before installation which would be completely unecessary to clairfy if ICE just shifted down. p13: (When installing ice, the Corporation can first trash any ice protecting that server in order to reduce the install cost. Then, he installs the new piece of ice in the outermost position in front of the server.)

It's clarifying that you cannot install into the place where the trashed ICE was; that doesn't mean that you're actually creating a permanent 'space' there. In fact, the fact that you MUST install in the outermost position means any 'space' there is meaningless.

ICE cannot be rearranged or moved similarly is referring to the fact you can't move ICE from one server to another, or swap positions within a server (barring special card effects like Sunset of course).

Let's engage in a slightly ridiculous example - there's nothing anywhere in the rules that states I have to arrange my ICE in a uniform manner - only that they are placed horizontally in front of the server they're protecting. I install two pieces of ICE in front of HQ. Then I install a piece in front of R&D.

Next turn I install another piece of ICE in front of R&D, but I place it leaving two whole card-widths between it and the other piece of ICE on R&D (in what, if I was following the conventional method, would be position 4 from the server). What position is this ICE in? How about if the one that was placed first later gets trashed?

How about if I start installing ICE so that they're staggered, leaving half-card widths in random places?

The innermost spot on a server means the innermost piece of ICE. If you're not satisfied with this interpretation, then your only recourse is to petition Lukas directly, as you won't find a rules citation anywhere that will satisfy you - it's never NEEDED to be stated.

You'll find the rules question link at the bottom of this page.