I wish I did...!
Depends on what you're after, and what you've got to play with, but a couple of things that may help... butt length is usually around the same distance as holding the hand on the pistol grip and placing the butt in the crook of the elbow. Can be set slightly shorter for standers, but for scoped rifles this can upset the eye relief, so this becomes a little tricky to adjust on the line.
Depends on your experience... if new i'd advise setting up around your main position... in FT you can adjust, which means you can shift the butt up and down for standers and kneelers if you wish. (not sure if HFT allows stock adjustment or not).
If more experienced, there's a growing trend to set-up around the weakest position and allow the greater confidence/capability to overcome deficiencies in the others.
One catch is that the more specific you setup for a position, the less flexible it becomes... so neccessary adjustment of the stock or accomodation on your part increases.
Wieght is as a rule has the balance point where the forearm supports. Was a trend to have it slightly forward of that, there's now a trend in 10m standing to have it slightly on it or even behind. I'm still working out how weight affects things, but it seems that having weight on the extremities seems to be more stable than the same weight pulled to the centre, even if the weight and the balance point is the same. Playing with stick-on wheel weights is a cheap way to play with it, and you can just use elastic bands to hold them on before committing to peeling off the tape.
I'd setup so it's comfortable. I've just setup my rig for winter league and the scope is way high, hardly any fore-end and the weight is low, offsetting the scope... and it now feels comfortable in all positions and quite stable, as opposed to my current rig, which only feels good in one. Still early days though.
Interesting subject, there's got to be a wealth of experience out there... bet the stock makers know a lot more than i've stumbled across.