Mike, I have both d7000 and d7100. They behave differently when using bbf. The d7000 responds to menu A1 and A2 in regards to bbf focus. Most people go with release priority so they can gain the affect of af-s or af-c using the technique. Hold the button for continuous focusing or press and release for a pseudo af-s mode. Now on the d7100, Nikon has decided that you WILL go with release priority. With the back button set to AF ON, the camera behaves as if it is set to release priority and ignores A1 and A2. This is described on page 77 in the manual. So I think you are stuck with that behavior.
Thanks Nick,can i be a pain and as you understand the differences ask you to have a quick look at a D7200 pdf and see which option Nikon have gone with for it,i am really enjoying BBF but not the delays due to incorrect focus with the BIF.