When you look at the path profiles of
KGO and
KNTV (simply click on the call sign listed on your TVFR) you can see that terrain poses some difficulty. Your description and your TVFR both indicate that raw signal strength is not the problem (which is why amplification did not help).
As an experiment, you could try lowering the antenna to within a few feet of the ground, where it still has an unobstructed view of the ridge top south of your location. (The purpose of the experiment is to determine if the signals of these two stations are less affected by multipath close to the ground. You may find you'll have some trouble with one or more UHF signals during the 'experiment'.)
A separate high-VHF antenna or a
ganged/stacked array may be worth considering also. I think it's more practical to try adjusting your existing equipment before resorting to the additional expense and complexity though.
