You wrote, " . . . I then experimented and created 3 tone curves with resulting histograms that matched almost exactly the histograms created when setting +0.3, +0.5, and +0.7 EV corrections with the normal tone curve setting."
Is there a difference between using the +0.5 ev custom curve (without using any exposure compensation), and using the default curve with a +0.5 exposure compensation in the camera? I can't tell from your description, but it sounds like you end up in the same place If so, why wouldn't one simply just set the camera's exposure compensation function?