Let me make something clear.
We can look at "efficient shot selection" all we want. We can deem shots lucky or unlucky based on the numbers. If a team makes a bunch of long-two's against the Rockets, it would be easy to say that the Rockets simply got unlucky. A long two-point shot is the least efficient shot in basketball. It's the very shot that the Rockets want to see the opponent take, unless the opponent is Dirk Nowitzki.
But here's the thing: an open shot has a good chance of falling from anywhere. Andray Blatche can make an open three if you give him three seconds to get set and shoot. Yi Jianlian can make three straight long-two's if there isn't a hand in his face to distract him. These are NBA players. They are not high schoolers or DJ Mbenga's. They are professionals, and for the most part, they will make an open shot.
It's easy to say that the Rockets have been somewhat unlucky, as opponents have been shooting well from long-two-point range against Houston thus far. But it's only an inefficient shot if there is a defender present and in position to distract the shooter or potentially alter the shot. Otherwise, there is no point in playing the percentages, and there is no excuse for seeing so many jumpers fall. An open shot, in most cases, is expected to fall, especially at this level.
The Rockets have been leaving way too many people open. It's one thing to "force" an opponent to take a shot from a certain area on the floor, but you've still got to play good defense and close out on the shooter.