OpenX ad server and Drupal - how to serve only one banner per page?

I have an OpenX ad server installed, but for some reason I seem unable to instruct it to only display a single banner per page in Drupal's summary pages (eg drupals front page).

I have the OpenX php snippet added into my themes node.tpl.php - the idea being that I want the banner displayed directly underneath the content, but before the following comments.... and then on the summary pages where 10 nodes are simmarized, it will just display one on the first node, and not any others below it.

Despite the fact that I have tried in OpenX selecting the options which seem to be designed to do this, no results?

"Don't show the banner again on the same page" and also " Don't show a banner from the same campaign again on the same page"...

Any ideas?