there are many factors other than simply dish size that can make reception troublesome.
- LNB(F) used (some are better than others)
- sat being looked at.
Example: you can find out how "strong" a satellite you are looking to use from Lyngsat:
Galaxy 13/Horizons 1 at 127.0°W - LyngSat Maps
Look at it's "footprint" and how much signal (ERP) is being splayed onto where you are. So it would seem in FL the signal for HBO on
cband should be pretty good.
Another issue with smaller dishes is co-satellite interference. The C band signal from a co-located sat (ie: one at 127W and 129W) might interfere with each other. THe smaller dish's view will see both of them at the same time, where the bigger dish could discern the beams better.
So will a 6 foot work? Yes. Will a 8 or 10 foot work better? most likely.
If you are doing this for fun - put in the 6 footer. If you are doing this for serious TV work - get the biggest you can afford, find, install. I think you'll be happer in the long run.