4 tuners, quad LNB, different number of channels

Hi there,
I've just finished installing my new 6981 and 8920 cards and have noticed something strange in DVBLink TVSource. Each card (including the existing Tevii S660) pick up a different number of channels.
At the moment, I'm using the latest drivers for each card which are hanging off a Zinwell (Mk4 model number 13822) Quad LNB:
8920:1.0.5.6
6981:2.0.0.12
S660:5.1.3.0 (beta).
The S660 seems to pick up the most channels at 923, then its the 8920 at 914 and finally (and the strangest one), the 6981 with 868(A) and 844(B).
I'm using whats known in the UK as a Zone 2 dish (instead of a Zone 1 which is the usual type in use in England) which is larger than the standard UK ones (designed for fringe coverage areas like Scotland).
Can you shed some light on this please as it a little confusing that there should be so much difference between them (especially the 6981's twin ports).
Thanks
Dave
I've just finished installing my new 6981 and 8920 cards and have noticed something strange in DVBLink TVSource. Each card (including the existing Tevii S660) pick up a different number of channels.
At the moment, I'm using the latest drivers for each card which are hanging off a Zinwell (Mk4 model number 13822) Quad LNB:
8920:1.0.5.6
6981:2.0.0.12
S660:5.1.3.0 (beta).
The S660 seems to pick up the most channels at 923, then its the 8920 at 914 and finally (and the strangest one), the 6981 with 868(A) and 844(B).
I'm using whats known in the UK as a Zone 2 dish (instead of a Zone 1 which is the usual type in use in England) which is larger than the standard UK ones (designed for fringe coverage areas like Scotland).
Can you shed some light on this please as it a little confusing that there should be so much difference between them (especially the 6981's twin ports).
Thanks
Dave