telling twins apart (movement) 28 weeks

So I just hit 28 weeks with twins, but it seems like the last week I have been having a hard time telling their movement apart from one another.  I used to be able to feel baby A low and more to the left and B on my right side.  But now that they are nearly 16 inches long how do I know who is who? I mean can A be stretching out into B's space?  I feel kicks constantly and know for sure when it's baby A but I'm starting to think A is taking over and I can't feel B as much... Any help or advice appreciated!