No, only the world background shader is affected afaik. If you have large unblocked windows the portal style guidance isn’t really needed - a lot of the background shader is “found” randomly anyway for its direct light contribution. I don’t know how the renderer does it, but it would make sense to me that direct contribution by the sun is traced the opposite way - is there anything blocking the sunlight if I trace the sun vector from the pixel?
I did some tests, and you need to have significantly blocked windows (partial curtains, tall fences, close neighbor house) for portals to have sensible effect on resolving the background shader. If you add a sun to all this in all it’s mighty power (I’m using sun 4500K strength 441 and sky texture 29 strength), it’s likely to drown the contribution from the small openings. The indirect contribution from the sun is going to create a lot more noise than the small openings (at least on fairly bright surfaces). This is from a fairly brute force point of view, in reality you might try to do some fakery and optimizations.