Honestly, we probably won't address it too much, particularly if Ray is back (because it'll force us to play a lot of small ball).
Part of the problem is by design (Doc telling the players to get back on defense instead of crashing the boards), part of it is a product of us relying on so many jump shots (and consequently spacing the floor), part of it is age and lack of athleticism, and part of it is effort and personnel.
Only the last part is really able to be changed, and given how this team is constructed and what we have left cap wise, I don't see a lot of room for growth.
Sullinger could help, but he's going to have to get minutes. Bass should start at the 4 and Green should get minutes there. That doesn't leave much time for Sullinger. And while Sullinger could play the 5 next to a taller 4, Green and Bass don't fit that bill, making it very difficult for Sullinger to play next to anyone but KG (which essentially means he's limited to only what's remaining of the 4 minutes anyway).