Welcome Alasdair!

SWIM says she thought she had broken through a few times before she actually did.  In her experience, she could not mistake what breakthrough refers to after it happened.

Amount differs for everyone, and a reverse-tolerance appears fairly common.  Leaf bed method should definitely work.  Just commit to having a break through, load up 60mg's.  Pull slow on the bong for two full breaths, holding each as long as reasonable.  On the third one, go for clearing it.

Best of luck!