This is the terrain profile for WCAX from tvfool:
http://www.tvfool.com/?option=com_wr...dALLTV%26n%3d7
This is the profile using different software:
The WCAX signal passes over two ridges, which causes scattering, resulting a non-uniform field as you saw on the hdtvprimer page. Point A is further out; point B is just before your antenna. I can see the ridge at point C behind your house. Using "what if" height changes on the interactive map browser:
At 115 ft 1Edge NM 17.6 dB; the signal clears point B
At 485 ft LOS NM 41.0 dB; the signal clears point A
What bothers me is, if the terrain affects WCAX, then why doesn't it affect WPTZ?
I suggest you hunt for a good location for WCAX (somewhere on you property even if it means a mast behind the house) using the HDB91X with the front of the antenna tilted up (15 deg ?) to catch the signal coming down from the ridge. You need to get the antenna as high as you can because there is a lot of ground clutter on the hill just in front of the antenna.