How does Yasuo's flow shield interact with runic armor?(If at all?)

I don't know if it does or does not currently (because I don't think Morde's was working correctly either), but hypothetically it should. The way it would interact would probably be that flow generation and quantity remains the same, but when the shield actually procs it gets increased by whatever percentage.

I don't play Yasuo, so I can't say this for certain, but that is how it ought to function if it's working correctly.

I don't see why not seeing as how it is a shield