Shorter is better for HD use. That extra 1.5 inches is not an issue untill the last inch of it hits a corner of a wall as you try to turn to address a threat. Hall ways and doors are not friendly to long guns so having a long gun that is as compact as you can have is the best option.
I can not even try to come up with any scenerio in my home when a couple of shots will not eliminate a threat. With this said, the extra ammo is not essential to an HD weapon.
If there is ever a break down in civil order, I have other weapons that will move from the gun safe to my bedside.
You are right on track with what I tell my clients about using a shotgun for HD. You came to these conclusions based on your own expirience with your current weapon and should go with what you have decided to do.
J.D. McGuire, Owner
AI&P Tactical, LLC
Remington LE Armorer
Mossberg LE Armorer