One of my players made a character who's a 2ft. tall gnome artificer. He just created a bag of holding as his wondrous invention, but the exterior dimensions (2ft. wide by 4ft. deep) is bigger than him. So I decide to make it a drawstring backpack with a 2ft. mouth so he still has the same insertion dimensions, and 1.5ft. deep so he can wear it like a backpack and not trip.
Does this change anything about the bag mechanically? Does this seem like a reasonable change?
The description of the Bag of Holding states (DMG 173-174):
If the bag is overloaded, pierced, or torn; it ruptures, is destroyed, and its contents are scattered in the Astral Plane [...] Placing a bag of holding inside an extradimensional space created by a Handy Haversack, Portable Hole, or similar item instantly destroys both items and opens a gate to the Astral Plane.
This suggests that the interior of the bag is a confined space/pocket dimension within the Astral Plane, and that the mouth of the bag is in essence a portal to this space. Thus, it should not be affected by the outside dimensions on the Material Plane.
