Well I must admit that is better then the idea I had by a good deal in some senses (idk why a sniper may want to get close but then again I seen people try to snipe with shotguns in games) .
Also, you can absorb the blast from closer enemies, get some altitude, switch to rifle-mode and blast a few charged-up rounds at enemies farther away or the larger one, weakening them before they get close.
If you're with a shotgun and an enemy that isn't too larger bashes away at your shield and you let it, then that enemy will be in for a nasty surprise, once it stops for a second. *blast*