The exposure doesn’t change the EV outputs because they’re the lighting/surfaces *before *exposure. The EVGRY(EV100 if using the default UE4 shader) and EVLUX values are the specific exposure values you can use based on the measured surface and lighting. EV is covered here Exposure value - Wikipedia and how it correlates to the amount of light in the scene Exposure value - Wikipedia
If measuring on a white card, EVLUX tells you the nominal exposure value necessary for the amount of light hitting that card. You would place the card in an area where you want to expose for(in direct light, in shadow, etc). This is the behavior of an incident light meter used in film/photography where you expose for the light and not necessarily the surface.
EVGRY will provide the exposure value to use to make the surface middle gray. If measuring something brighter than 18% gray, this can have the side effect of making it dim and conversely if measuring something below 18% gray becoming brighter - just like a real camera’s auto-exposure. So ideally this value is only used if measuring an 18% gray card. This is the behavior of a spot meter, where you’re exposing for the surface based on the lighting.
Once you have that EV, you plug it into your Post-Process Volume, camera, or viewport. The PPV/camera will default to not expressing exposure in EVs, so you need to have Extended Luminance Range enabled in the project settings.
So, let’s say with the EV of 2, you might use a min/max EV of 1/3 respectively, or if you measured in shadow and got a -2, you could do -2/2. It’s up to you how much you want to under/over expose, but the provided EV values are the “correct” exposure depending on what you measure.
There’s no simple way to blend unfortunately. You just rely on the PPV blending or use a wide enough range to allow adaptation in most situations without the need for adjustments.
And exposure compensation defaults to 1 in 4.26, it should just be set to 0 unless you specifically want to add an additional compensation value.