The time is playing the main role in my case. When my flight time is under 3H, I have no problem at all regardless of the area I’m flying. Example: My return flight from PANC to KDFW. The FPS is always high high when I’m Flying over JOH with the exact same setting and the same altitude. So, same area, same TLoD, same airplane, the only different is the flight time. From KDFW to JOH is almost 5H 30 Min and from PANC is about 15 Min. I do understand flying to some areas with more objects/details can cause performance degradation but, it should always be the same not changing based on the amount of hours you’re flying to reach that area. In my case I’m 100% sure that the combination of the Terrain Level of Detail and flight time cause performance degradation.
Attached picture is my last flight from KDFW with Ultra settings and TLoD setting on 100.