Hey FacePalm,
DistanceField meshes are how DistanceField shadows are calculated.
There are limitations with everything including shadows and DistanceField.
If you could recreate this in a test project in a later build. Like 4.8. I know that the performance of DistanceField AO especially has been improved by up to five times in the preview of 4.9.
At this point this is not a bug because you are able to slightly improve this issue with a FOV change.
With the limitations of the current version of UE4 that you are using I would highly recommend testing this out and seeing if that fixes it.
I will be moving this thread from Bug reports to Rendering,
Thanks,