Is this with D3D9Client or with inline client? Could you send me the test files to check for myself?
It is the standard orbiter. Not the D3D9 ( that i cant experiment cause there is not D3D9 actually for XP. Jarmonik, if you read this...

)
No, everything I wrote yesterday, ( cf: Hymalaya ) was only a hypothesis, In others words: what could i do if...?
But I was trying this morning to really experience there. I will try to find the files that I used for Heathrow last year but I have already done this morning the test at Mount Everest. To to see.
I will attach the files of this experiment in a following message but I give you a first overview:
Here a level 0 tile ( Earth_0_e0123_n0039.dds mipmaped - dxtbmp) in a cfg (Baikonour renamed Everest) at Mount Everest. Unlike the observations I made on Heathrow (*), this time, the tile is at the summit of the mountain, flat for its entire extent, with geometric effects little readable vis-a-vis ( in interference ) with textures of the Surf folder.
(*) but when standard tiles in a cfg interfere with tiles from the Surf 2016 folder and if the elevation is low, it is not easy to distinguish what is on or below. However, even for Gran Canaria, although at almost level 0 for the runway, one can see from a certain angle, grazing, sometimes the textures of the cfg, sometimes the textures of the Surf folder.
Here a level 5 surftile ( Earth_5_e3956_n1273.dds mipmaped - dxtbmp). Curiously, the object, hangar, tanks..., seems to match / to be on the mountain itself.
The files for Everest in the next message.