Yes Rama was 31 miles, I doubt Ray or anyone could state as fact they are not simply biospeheres.
If they are , then their size may have nothing to do with us or any agenda here, they could simply be the habitats of a nomadic spacefaring species.
On our own oceans we have huge vessels that transport large quantitys of cargo, like coal or oil, but we also have ships of similar size whose function is to transport people, thus size is not necessarily an indicator of function
I guess a 14 mile long structure could contain several biospheres and a few of these other large machines. Of course their design specifications carry some information about their intended purpose. You've already pointed out the obvious one, they are transports. Large transports carrying smaller transports.
Ray apparently has much more than just information about their size. That data may contain some further clue or it may not. Do they appear to making changes to the environment? Are there things they
always do? The
compressed time thing suggests to me that they are doing much more than can be casually observed. Since Ray is heavy into instrumentation it seems like there may be some clue in that aspect as well.
Here are my
flying by the seat of my pants largely unsupportable hypothesis of the morning:
The large cylinders are interplanetary transports and possibly processing facilities or refineries of some kind. The smaller vehicles brought here in them are performing the task at hand. Popular UFO mythology suggests that they are here primarily to interact with human beings but may also include other animals and plant life on the planet. This appears to have been going on for some time, so it could to be either a
maintenance activity or a very long term project.
Since there are no reports of large mineral deposits being mined by mysterious unknown parties and people do not appear to be disappearing in large numbers the idea that they are here to get something and take it back seems less likely. This makes a maintenance activity or long term engineering project more likely. As it seems these things operate on the fringe of our perception, the actual
locus of their actions could be as well.
And now, back to reality where ...
There are no UFOs in the sky here, only dragons. I'm taking a short cut through a frozen forest over to a mountain pass, hoping against hope not to run into another damn troll or Sabre Cat. One of those freaking monster cats killed my horse and I torched my traveling companion fighting a Troll/Yeti thing just hours ago. Note to self, "Don't step in front of a panicking novice spell caster." Now I need to get somewhere and unload some of this loot I'm dragging through this f'ing blizzard before another dragon shows up. I should have never wasted all that gold on that useless horse. Never again. I'm buying something I can kill a troll with. Something like a super-duper flame spell of some kind or maybe a strong poison. Yeah, that might work. Oh crap ... what is that up ahead? Save, save, save!