Shortened fork oil level

So from the replies I got, it sounds like less of an exact science, so I'm going to start on the low side, do some road testing to see how easily it bottoms out say, when braking and hitting a bump, and slowly add oil until it either won't bottom out or at least takes quite a bit to get it to.

It'll probably be a slow process but I'll post what I come up with in case it's of use to anyone.