This what the terrain profile looks like using a different software:
scroll half way down this page to the Example of a path profile diagram and you will see how refraction bends the signal down
http://www.mike-willis.com/Tutorial/PF6.htm
If there is a temperature inversion in the bowl between the transmitter and the peak, the signal can get trapped in a high altitude duct and not be able to bend down to your antenna. Scroll down to An illustration of a high-altitude tropospheric duct.
http://www.dxfm.com/content/propagation.htm
The only thing I can think of at this time would be to tilt the front end of the antenna up to better catch the signal coming over the peak. However, if the antenna is old, it might not be performing as well as when it was new.