Dave,
I asked a similar question on the dbsdish forum (
http://www.dbsdish.com/) awhile back -- can't retrieve it for you, since they only archive messages for 30 days. Post your question there and you'll probably get a good response.
-Ken
PS-The answer was that voltage drop (not signal loss) is the problem with a long run. The switches need a certain voltage to function and it appears that at least some of yours aren't getting enough juice.