Thanks for the info. No, you are are not going to seeing much improvement from increased height as your location is already clear of obstructions. On heywhatsthat I raised your antenna by another 50m to see how that affected things and your range increased by a very small amount.
Current maximum range...
After adding 50m to the height...
This is the edge of what you might see if it were at 40000 feet.
Reagrds,
Martin