Hi Twibbz -
Auto Exposure pulls it high and low percentage values from the scene colors luminescence histogram. It might be worth the effort to play around with some of your post process settings other than Auto Exposure, like Tonemapping and Scene color. Adjusting these settings may help equalize some of the dark settings in your scene. You might also want to try to add a skylight into your level without shadows which will provide a little bit of light all over.
https://docs.unrealengine/latest/INT/Engine/Rendering/PostProcessEffects/AutomaticExposure/index.html
https://docs.unrealengine/latest/INT/Engine/Rendering/PostProcessEffects/ColorGrading/index.html
Thank You -
Ketchum