Now I'm having second thoughts about posting this curve first. It might be confusing on its own since it does not show the effect of flare on an exposure of a full scale subject. This test only shows the effect of flare on a single tone. Showing the effect of flare on a full scale subject would illustrate that you cannot "counteract" subject flare, and reducing exposure does not help (in fact it can be detrimental). This was the point I was trying to make in the other thread but now I may have confused things for people.
Regarding lens masking, I made an attachment for the front of the lens that reduces the image circle to a rectangle the size of the 35mm frame. This prevents most of the flare that might be caused by extraneous light bouncing around inside the camera.