[2.0.62] Build order affects belt throughput of direct-to-splitter mining

[HeliGungir]

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Mining to splitter build order bug.zip

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Context:

At high mining productivity, mining directly into a splitter is one way to increase the drill's output. The splitter must be oriented perpendicular to the miner for this to work.

Expectation:

The left copy of each mining drill is outputting a full belt, which is the expected behavior. This happens when the splitter is built after the belts, or during the same tick as the belts if I pause the game via the editor.

Bug:

The right copy of each mining drill is not outputting a full belt, which is undesired behavior. This happens when the splitter is built before the belts.
All variations of rotating, flipping, and using copy/paste/undo seems to be consistent with the above observations.

Related:

Inserters also drop items more quickly to splitters than to belts. The throughput of this was lower when 2.0 came out, and when this was reported as a bug, the old 1.1 behavior was not considered sufficiently "expected behavior", so it was not restored to 1.1 speeds. I disagree with that decision (suggestion thread here) and I certainly do not want a similar "fix" to direct-to-splitter mining.

[Magistrat]

I did some testing on 2.0.64. I can confirm that the splitters get faster when you replace them manually.

But when the belt flow stops once and continues later, the splitter is slower again. Wich would be the same as building the splitter first and belt connections after, as in the bug report. There was time for the ore to build up on the splitter parts.