I don't have the backpacker2, but i've got a different branded pretty much the same turkish shotgun with the 20" barrel and from what i've seen with mine it matters less on the barrel length and more on your choke.
You're really only losing like 12"-18" depending on your barrel length from your shot spread cone vs a longer barrel, so try taking a step backwards next time you pattern your gun and see how much of a difference it makes.
Now when it comes to the chokes that come with these guns, they can be hit or miss, but the same can be said for any choke. You'll have to try a few out and pattern the choke and see what your gun likes.