bit of both for me... the gun sits on the knee but it's stabilised by a hand that wraps around my knee and holds the gun. I can vary the contact on the knee as it suits me and the target position.
There's no right way of doing it, just ways for you that are better than others. Some shoot over the arm for instance.
BFTA/NSRA County Coach
CSFTA Chairman/BFTA Rep