While your results are exactly as I would have expected (for all of the tech support reasons given). Indeed, height is might when it domes to these UHF signals. I am sorry to hear your results were so bad but would advice you to take the advice mentioned above and return the unit to Winegard as quickly as possible. You will, of course, now have to seal up the holes you drilled and re-install the Sensar antenna which will be a bit of a pain. I hope you kept all the parts!
Someone above mentioned the Rayzar Air. I installed one of these on the same mount as my Sensar IV and while it's not quite as good for long range, it works as well or better than the Sensar for TV stations within a 30-40 mile range since it is bi-direction allowing reception from the front and back. I did this back when I worked for Winegard and used it for testing. I mistakenly threw away some of the Sensar parts or I would have re-installed the Sensar IV as you simply cannot beat it.