It's a decade ago I purchased the FastExt lib, I didn't even remember they had this. But yes, the alignment of the effect should still be fixed, it's not logical by now. If the effect is fixed to an object like the sun, you can lower polycount and texture size of the ray mesh. But Somehow I like the screen filter approach, that fixes the filter to the camera. It just really needs a fix that adjusts the angle and position, so certain camera motions don't make it look unlogical. Right now I am more concerned about optimizing the render time, fixing the effect angle etc. I save as the easy part as a dessert.
Also, small texture size causes flickering rays because of marching pixels (and the KIND of pre-mipmapping in the dds texture has an impact, masked textures flicker more with the sharp "next neighbor" method), a blur of that render might fix it, but it's costly, or yet another challenge.