Hi! In response to your question, you might feel it in your lower back a little, however, you should really try to focus on squeezing your glutes. You may want to try some different positions on the ball--either further back (towards the end of the ball) or further up so more of your abdominal area is covering the ball. Try to see which position gives you that better squeeze. Hopefully this helps
I agree with Kristen about repositioning on the ball to find the right spot. I didn't feel anything in the glutes at first and I repositioned and now I feel it. I also have to concentrate on squeezing the glutes as I start the move or else the back seems to take over.
Also, try to pay attention to keeping your core strong, as your abs can help support the lower back, and keep it from getting too involved, during the move.