So, I have been having correspondence from someone who has 3:16. They asked:

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>>>The aliens NEVER move on the range map.
>>>Only PCs move on the range map.
>
>Interesting. Why did you rule it like that?
>Any particular reason, metagaming -wise,
>why the aliens' counters don't move?
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Why did I rule it like that? Because it works and it's elegant is my answer.

If you were to have a range map (or a free-form map) that contained both alien counters and PCs then that's fine too... but all you would be doing when determining range would be finding the difference between where the alien counters are placed and where the PCs are placed. This is how wargames work, how most role-playing games work (how far is the enemy? which range is that? what is the modifier? and so on). D&D4e uses squares to make the counting easier I guess.

Anyway, that is inelegant. Since we are always measuring the distance to a fixed target (the aliens) we can simply set them as a fixed point (an "observer" if you will, in physics terms we're setting a reference frame). Everything else is measured relative to that fixed observer. So, *fictionally* we are now given a free hand to describe where the aliens and PCs are, since *mechanically* we know which "range" they are at relative to the enemy threat.

Can the aliens move? Yes, they can. But when they move in the fiction their position on the Range Map stays fixed, and it is the PC counters that move relative to them. We only care about the range of the PCs relative to the aliens.