That is normal behavior for miners. Big or small, vanilla or mod, miners drop ores onto one (1) side of the belt.
It's not a bug, it's not incorrect, it's how things normally work.
That said, when you have a miner that is capable of producing more than one lane of a blue belt worth of ore, it's natural to ask the question "How can I get a full belt's worth of output from a device that will only output to half a belt?" In fact, it's so natural that one might consider it a frequently asked question!
The standard answers to that question are:
Instead of having the miner output directly to a belt...
- Have the miner output into a logistic chest (logistic robot throughput scales with number of robots)
- Have the miner output into a regular chest and use loaders (mods) which can saturate a belt.
- Have the miner output into bigger chests (mods) and use multiple inserters/loaders to transition to belts.
- Have the miner output into a railcart and use stackinserters on those (like above, but minus the mods and plus some train shenanigains)
Note - these answers pertain to vanilla miners with crazy modded speed/productivity modules, to miners from this mod, and to high-speed miners from other mods. Because this is normal, non-buggy, correct behavior.
