Auto-guns are easily eplained.
Syn-tec hacked some Nian robots from earth and used them to develop auto-cannons as these were weapons they were comfortable with, opposed to the yet unresearched missile, laser and EM weapons. The Nian robots that were still antonymous of course noticed these weapons and as any scientific society ( which the Nians clearly are due to their advanced robotics, weapons and more. ) they would research these weapons. Research that would be stored in their kernels.
Field containers are also easily explained. Notice how when you use a teleporter or a terminal your robot is changed into some for of lightning/energy? I'd say this is clear evidence that Nians have mastered matter to energy conversion and back. So maybe a field container is not an actual earth container but instead a battery. Matter is converted into energy, then stored in the battery and later converted back. As to why it's so much larger then the Sequer, maybe the Sequer uses only a portion of it's frame for storage. Engines, Accumulator, Armor, CPU. Reactors, Modules and who knows what else all require space. So in the end there may not be that much space at all left for a matter battery to hold the storage. Add to that that in a field container all systems are directed to storing matter while in a Sequer systems also need to monitor Armor, Accumulator, Propulsion and much more.
As for robots not bumping into each other can be explained with the same theory. Nian robots can convert matter to energy and back. So maybe when 2 robots collide they can quickly convert parts of themselves into energy and then just as quickly convert it back to maintain structural integrity while the other bot this time converts it's matter into energy. Of course then why can't robots pass through the ground. Well the lore says this:
"Due to the planet’s dense core and the relatively fast rotation, the electrostatically charged oceans dividing islands are impenetrable barriers to every object driven by electricity. On land – contrarily – life flourishes."
So water in Perp is electrostatically charged. Nia is supposedly very similar to Earth, so it's safe to assume that the ground would also contain water. It would have to be for the plant life. This water would probably be a lot less electrostatically charged, but still enough to screw up any robot's matter to energy conversions that wanted to actually pass through the ground.
There you go, explanations about as good as you can get I think. Should be on par with your average sci-fi novel.
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