Crook of the elbow has served me well, just as 1 1/2-2" from nose to knuckle is another, but they are just rules of thumb for LoP, and LoP is just one variable in a whole bunch of them. Proper fit is a complex subject, but can be as simple as "It feels comfortable, puts the rib centre and just under my eye every time, and I shoot it well, consistently".
RG