Here is Boxerfan's report at 20 feet. I went to the trouble of remapping his virtual channels to real, then wnet down the table of the TVFool report to see how his results matched. Overall, his results agree quite well, as all his "good" channels are predicted to have 0 or better Noise Margins. His "weak" and "poor" stations are all 2-edge paths with -12 or worse Noise Margins in the grey part of the table.
Boxerfan, I would say that you are doing as well as you can right now. I seriously doubt that you can significantly improve the reliability of the weak and poor stations - there's just not enough signal to be had.