I am in the middle of implementing stochastic screen space reflection based on frostbite presentation here. On page number 39, it is stated that we need to reproject the ray intersection location instead of the reflected surface location. I don't really get what's the difference between the two. Isn't ray intersection location the same as the reflected surface location. Can someone explain this?

I am in the middle of implementing stochastic screen space reflection based on frostbite presentation here. On page number 39, it is stated that we need to reproject the ray intersection location instead of the reflected surface location. I don't really get what's the difference between the two. Isn't ray intersection location the same as the reflected surface location. Can someone explain this?

And then in another ppt, they mention that

I mentioned temporal reprojection, so let’s have a quick look at it now. The idea is simple: given a pixel’s 3D coordinate, check where it was in the previous frame, project it, and we have the texcoord to sample.

… except when we move the viewport, reflections exhibit parallax. That is, the reflected objects move according to their depth, not the depth of the surface which reflects them. Attempting to reproject reflections using the closer depth results in smearing. So we calculate the average depth of the reflected objects, and reproject using that. This results in much reduced smearing.

Again I don't understand this at all.