I've determined for my needs that "placing your stock in the crook of your elbow" is completely useless.
Have you read the article by Bill Hanus on LOP? He, and Phil Bourjaily both use the "eye to thumb knuckle" distance as the most relevant measurement... that being, a pretty broad IMO, 1" ~ 1.5".
In either case, it requires a second party to take that measurement for you... it' seems that most knowledgeable sporting shotgunners use this, or a variation of this, method.
I've tried it a few times, but I think that as I tend to take a more square (too square?) to the target stance, I find that my happy LOP ends up being a bit shorter for my height at 13" rather than the minimum 13.6" the above method suggests.
Rudy Etchen said... “You should shoot the shortest stock you can shoot without getting your nose kicked, because the farther you are away from the gun, the more you have to steer it. The longer the gun is, the harder it is to point. If you're tied in close, not getting your nose kicked by the thumb on your trigger hand, the better you'll shoot.”
In other words, if there's a hard and fast rule that works for one and all, I'd love to hear it.
C