Exponential Height fog 'pops in' at a distance

HI, I’m working on what is basically a large world machine type flythrough using sequencer. Every time the camera gets to a certain deeper distance, focused on a far away vista the exp height fog pops in, to a higher key level. The issue is that no matter what the distance / height settings are the fog will always pop in / strobe a bit in these darker areas of the landscape. I’ve tried with and without the new volumetric option but the pop in area is the same, additionally I’ve tried with and without other effects, exposure, and making sure there are no abrupt keyframe changes in the area… many lighting rebuilds. etc etc. Does anyone have an idea about this issue? or how to set the engine to display fog in these deeper areas so it doesn’t pop in when the camera starts rotating ?