It seems to me that the important measurement is not that from butt to trigger, but instead from butt to where the trigger hand grips, as long as the finger will still reach the trigger. If the distance to trigger were so critical I don't see how one could shoot a double trigger as the distance between the two triggers can easily be 3/4" to 1", yet it is easy to do with a slight change in the trigger finger position. If you can reach the trigger and your thumb doesn't hit your nose, I suspect that shooters can adapt to a fairly wide range of LOP and it really isn't that critical and compensation can be made as discussed above. Eightbore's 13 3/4 to 15 3/4" is quite a difference, yet he shoots both successfully.
