Many of you were right, I had 37 miners, turns out only 30 are needed to guarantee 100% fill of the belt.
Also, I will try the design you showed for the smeltery.

I'll implement the design later and tell you how it fares !

Many thanks !

Dear community, I'm pretty new to Factorio, but I love it. I'm trying to set up my first base and I seem to encounter a problem in my iron ore extraction/smelting. The belts that feed ore to the smelters seem to be stuck in certain lanes, which creates problems for miners that need the space to put ...