Hi George:
Hmmm... Now, why did I already know you were going to post that, and why did I still not explain it in advance via my post above ?
I guess one just can't be thorough enough when you are participating in a thread, George !
So, even though I think it likely that you already know this, rather than leaving
other readers confused about whether, how, and when this actually happens, I'm going to go the extra distance and explain it here (...which I really should have done in my post above.

)
To see the initial "automatic" coupling of terrain mesh and texture slider change when setting texture resolution to 7.5 cm in the FSX GUI:
1.) Set FSX Menu > Settings > Customize > Scenery tab GUI sliders to minimum resolution settings for terrain mesh and textures
2.) Be sure FSX.Cfg is
not open in any text editor, so it "saves" parameter changes made via FSX GUI
3.) Exit FSX
4.) Restart FSX
5.) Navigate to:
FSX Menu > Settings > Customize > Scenery tab
6.) Set Terrain Mesh resolution to
19 M <
yep... 1 LOD short of "10 M" ! 
>, and Texture resolution to
7 cm
7.) Click "OK"
8.) Still in FSX, Navigate again to:
FSX Menu > Settings > Customize > Scenery tab
9.) Observe that
both terrain mesh and texture sliders changed when manually setting
only the texture slider to '
7' cm in the FSX GUI.
10.) Specifically, note that
terrain Mesh resolution slider changed to "10 M" when "OK" was clicked after Step 6 above
NOTE: Obviously, the FSX Scenery display slider can be manually set to an even higher terrain mesh resolution
AFTER one has had FSX "automatically" apply the initial 'required minimum mesh resolution' parameter relationship between the terrain mesh and texture sliders for a texture resolution of at least '
7' cm via the FSX GUI, as we see in your screenie above.
Hope this helps those considering these numeric relationships as a basis for use with higher resolution FSX.Cfg scenery display parameters !
PS: Thanks for keeping the bar set so high for "thoroughness" here at FSDeveloper, George !
GaryGB