It's hit box. That combo doesn't work too well. You're standing just too close for BS A+B to hit. It's best to do BS 3B BS 3B BS 22B after BS 44A. If it's a RO that you're going after, then you should try BS 66K after you hit them with the first 3B. That one requires some timing. It also doesn't seem to work so well if you are too close to the edge.