But its very weird and obscure. With such a lacking in space, you have to run multiple train types and overlap them: either having mixed trains. And there's also the issue of "leftover" pieces staying on a stack inserter (ex: Stack inserter grabs 7 items, but then the assembly machine only accepts 3 of them, so now the inserter is "deadlocked" with 4 items. But the assembly machine needs another item, so everything deadlocks and shuts down).

There's ways to fix all these problems of course.

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But the easiest way is to instead use bots and/or belts to unload into the "last mile" going into the assembly machines. (Belt/bots can also reach 12 beacons per assembly machine if you're willing to have a faster, but more costly, design. Mainly for UPS wars rather than in-game benefits.)

But yeah, Trains are obviously the best bulk transfer item in the game. And while they aren't "unsuitable" for last-leg delivery per-assembly machine, its highly complex to do so. So its just easier to use belts/bots for that unless you're going crazy with UPS or something.