The 'elbow to trigger' reach only really tells you how it sits inside your elbow.....and nobody I know shoots one from there, but it is a quick reference that you always have with you to give you an idea how one 'new gun' compares to one you shoot well.
What you really want to know is how it mounts to your shoulder and shoots, for you, and that takes some shooting (usually) to find a fit that works for you, THEN reference that elbow to trigger finger to know how to compare with one you pick up.
British shotguns are often longer in that 'pull' than many 'made for the masses' and marketed here guns. They teach to 'throw the gun foward, pointing the barrel toward the critter and beginning the swing, then pull it back into the shoulder and continue'. It has been said that Americans (a nation of riflemen) tend to want to just slip the buttstock upward into the shooulder (too many years of shooting 'too short of pull' long guns?).
It is also said that fine tuning a stock can be as little as 1/4" this way or that (or for some even perhaps less).
So, FWIW, Ive been going with the longish stocks by choice and it is working for me, YMMV.