I once used a 14 foot mesh antenna on an offshore drilling platform in Alaska, to receive a C-band satellite that happened to be 0.13 degrees below the horizon. It was shooting out across water at sea level, and the dish was actually about 75 feet above the water. While the entire dish was definitely not illuminated, I would have to say that enough of the top of the antenna was contributing to allow a poor (but watchable) analog signal. It was very strange looking at the feedhorn from the back of the dish, through the mesh, and seeing that it was pointed into the drink, below the horizon...but still getting a picture.
One other thing to be aware of is that even on C-band, you will have problems with ducting of signals when weather conditions change. A real continuous problem when your elevations are less than 2 degrees, by my experience in Alaska. Nowadays you can hook up a free to air receiver, lock in a transponder/channel, and leave the quality meter displaying the signal. Very useful information can be deduced after analyzing a DVD recording of more than a few minutes' length.