Quote - According to Smith Micro iin an official tech support response: "One thing you could try is reducing the irradiance caching down to zero.

Thanks. I had tried reducing it to 50, and looking closely now I can see a very slight reduction in the over-shaded interfaces, but I'd put it back up to 90 because reducing it increased the render time dramatically. I'll give zero a go, and see whether it improves matters while still rendering in a finite length of time.