Sorry. I forgot to re-read your OP before I replied.
I would bump OLOD up to 200 if you have the headroom. It will NOT fix the issue entirely, but it will at the very least help to minimize it.
Also, you may want to play with dynamic settings as you can run your TLOD and OLOD at max settings whenever your are above your target FPS, and the PC will automatically lower the LOD settings when you are below your target. That will NOT fix your pop in issue, but it might get you 400 TLOD when you are flying over the country rather than landing at a big airport surrounded by photogrammetry. YMMV.