Quoted: The best way to check what kind of LOP you need it bymaking a right angle with your arm and placing the buttpad on your bicep and put your finger on the trigger (Unloaded of course) and you can find out if its to long/short/ or JUST right

That is an old standard shotgunner's test that does, indeed, work pretty well for many shooters if what they need to do is use the shotgun in relatively light clothing from standard sporting shooting positions. CQB while wearing body armor is a different thing entirely. For that, depending on the shotgun, the armor and the build of the shooter, you will usually need one to two more inches cut off of the "bicep" measurement.

The shortest LOP I know of in fixed factory-made aftermarket stocks is 12". offered by Hogue and by the short SpeedFeed with plastic buttplate. You can, of course, cut down your standard stock to whatever LOP you desire easily with a miter saw, although grinding the pad or buttplate down and re-mounting can be a PITA. (Some use gobs of silicone caulk or Bondo to run the screws into with the plastic stocks, but you still have to re-drill the holes in the pad / plate) You might see if you can find an old Express "boxcrate wood" stock to try cutting and use as a pattern. These stocks dry out easily and once they do, they invariably crack at the wrist under recoil, so there should be some out there for free if you look hard.

Have you actually tried a 12"? That is pretty darned short.