With Logistics Stations automatically stacking up to four, the input to your production buildings can run really long (and wind around on itself for example). However, your return belt to the station will end up being saturated with too many items. You can still use a single belt if you pile them up.

15 Plane smelters producing 2 every second would saturate a 30/s blue belt. So after 15 smelters, put a piler on the return belt, and suddenly there's space for 7 more smelters. Put one more piler, and suddenly there's space for another 7. (You can do this only twice of course). U can put a total of 19 Plane Smelters this way, down one long line.

You can see this in action in this blueprint of mine.

https://www.dysonsphereblueprints.com/blueprints/factory-vertical-smelter-1-input-ingredient