I do not know a lot about Norsat, I would stick with Eagle Aspen, Astroltel or Precision "digital and/or high stability" models. 15d C & .6db or less Ku.
I agree I would check for obstructions in the feedhorn, and the dish alignment.
Not sure where you are in SoFla but here is the
http://www.ses-americom.com/satellites/amc-7_cband_eirp_and_frequency.html]FOOTPRINT[/URL] for this bird, as well as a nice look angle
CALCULATOR. If you aren't having issues with other birds or channels I wouldn't mess with your dish's arc too much.