I have both, and the lavendar is not really leaf like, at least mine isn't. The lavender I have is more like small bits as opposed to leaf.
Therefore, if I was going to use the two, I would use more of the leaf like material, which would be the peppermint.............
The idea with the leaf is to light the side of the bowl, remove the flame, and inhale, letting the remainder of the bowl to burn without direct flame, but i don't know if the lavender, would keep burning as easily, once lit, because it isn't as leaf like as the peppermint........therefore i would vote for 2parts peppermint to 1 part lavender.
I, personally use Mullein, and have been using 1:1 with Mullein only.
Works for me.................
Good luck............
I am certifiably insane, as such all posts written by me should be regarded as utter nonsense or attempts to get attention by using totally fictitious verbiage...........
The above refers to the fictitious 'I'