On my last voyage foaf barely broke through, he was there but the visions didn't seem particularly bright, so once he was over the intial rush, say in less than a minute's time, he opened his eyes and went back to the pipe- the rest of the dose was still hiding within the parsley and topped him up and took him far and away.

Have you tried returning to the pipe once the initial rush has died down and the threshold visions have started?  It is quite hard to continue smoking when the rush hits you (in foaf's limited experience).