ad-hoc mode threshold problem?

Hi,

I'm trying to set up a prism54 card in our wireless community net.
It works fine if i test it at home, with some other ad-hoc cards in the
same room.

On the roof however, the card does not connect to the existing ad-hoc
network. It creates it's own Cell ID. Even when i can get it to
associate with a very nearby host (in fact, doing it the other way
around and letting that host associate with the prism54 already up), the
packages do arrive from the prism54 on the other side, but the packages
from the other side never arrive in the tcp/ip stack of the box with
the prism54 card.

This looks like some kind of threshold problem to me, where the prism54
card discards all information for low-quality links and apparently
regards our whole network as a low-quality link.

There's a lot of iwpriv controls for the prism54, but till now i haven't 
found an overview of what they do. Is there a list of their meaning 
somewhere?

Would some of the iwpriv controls be able to fix this problem? 
Does anybody know another solution?

Grtz,

Jaap