Actually, the "slightly outside the window" version is not good either, you will have a cleaner solution in areas where you hit the portal but the same noise level in areas where you don't hit the portal - so you'll have to wait more or less the same time until everything's clean.
Yup, that's why I wrote the prefect/good/bad marks. Maybe you are right it's not very good but from what Keymaster wrote it's a plausible method.
You can also use (singlesided!) glas windows as portal (the checkbox in the material) and you'll have glas + portal in one go.
Yes, but you usually put glass somewhere in the middle of a window hole and as far as I know you shouldn't use portals like this.
So where do you guys put the portal in relation to the glass? single or double sided. behind the glass or in front of ?
If you want to have a separate portal object and separate glass, you put the portal outside, like in my pictures. It should be a single plane with no thickness. Normals don't matter.
If you want to have one object which is a portal and a glass in one, then you should use a single plane with no thickness and give it a glass material with no refraction and with "is portal" checked in its material's advanced parameters. But it should also be placed like shown in my pictures (perfectly on the outside of the window hole, so it's not always possible depending on your project).
