I've asked this question a couple of times and got various answers. First of all, Richardson quotes a figure for the capacity of the oil tank which is completely wrong. I took my tank off and measured the total capacity and found that filled to the brim, it wouldn't take his amount. Sorry, I don't remember the numbers. Once I knew that that wasn't going to help, I put it to the back of my mind.
The problem I've had and others seem to have as well, is that there's a fine line between having enough for the health of the engine and having so much that oil spits out of the cap. I've resorted to using a spoke as a dip stick and keeping the level at halfway up the threads. That's with the spoke slanted into the tank as far as possible. It may be too low but hasn't caused any problems yet.
I've also played with various breather solutions and have what I think is a fairly good setup in that respect, but the oil tank is the weak link.