Paintings shape to the size of the space given to them on the wall. So if you're getting the bigger sized paintings, try putting a few blocks that stick out of the wall to limit space, then remove the blocks afterwards.
AHHHH!!!! Well Thanks! That makes sense, something has changed in the update though because I never used to have a problem placing paintings. I could group paintings with no problems that were spaced the way I wanted most of the time.