i think it depends also in the defense you are facing. If you go run and gun but you'r facing an opponent who has an awesome out def, maybe your pg/sg cant shoot well so your big guys enter (more) in the offense.
At least when i play Inside, depending on the defense the other team has, my PF/C shoot more or less...(but usually more than the small guys).
And my pg/sg playing inside, try to drive to the basket instead of shooting from a far range, wich is, as you said, reasonable.
What i dont know is if that drivings are calculated against the inside defense of the opposite pg/sg or his out def.