Unable to get 4 birds, while other adjacent birds are ok.

[videobruce]

There are four satellites I can't receive;
AMC 6, AMC 9, Anik F1 & Anik E2R.
The adjoining satellites are ok. Especially AMC 9, where AMC 3 & AMC 5 come in fine. AMC 3 is only 2 degrees away from AMC 9 and I get nothing.
I tried adding TP's from published listings, but still nothing.

Any ideas? I have a Invacom QPH-031 Quad LNBF & a Pansat 3500s receiver w/a Winegard 1 meter dish in the eastern US.