I know, I saw that thread. There are some mistakes in your assumptions. I haven't had time to go to that thread and respond. I have to do a lot of demo renders and shaders to show what is going on there.

Here's a render I just did, with an airplane over water. The reality is that the water is so bumpy no details can be seen on the reflection of the plane. So it really doesn't matter whether we get a secondary reflection off the cockpit canopy or not. This is rendered with only one bounce.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)