That is correct. I usually add two more exposures for artistic taste, specifically to get the brightest spots in the scene. When you do a baked reflection probe, you cannot edit them directly unless you do a custom bake. Coming from Skyshop, those exposure settings are helpful sometimes. You would have to have a well lit scene and great texture work to take advantage it. And the visual difference is very obvious if you use HDR externally vs. captured in engine. Most likely, the only external HDR people will use is a sky HDR... Having exposures on imported HDRs will be good, especially if they are initially dark. I will have to do some tests.