This was posted on Nasa Tom's site about the balance on the Racer and adjusting the arm cuff (I need to try this myself):
I've been playing around with my Racer and stock coil. Here's how I get the best balance. First I don't put my arm through the strap instead let my arm lay on top while the strap bridges the gap in the arm cup. Also pushed my arm cup adjustment all the way forward. What this pushing forward does is you'll notice the farther back it is the strap will be closer to your elbow where the meat starts building on your arm., thus the angle starts changing quite a bit (sliding forward causes the alignment between your grip and arm connection over the strap to be more inline, causing with detector to feel less nose heavy) . Overall this is what feels the best overall for me. Folks you may want to try. And yes your mileage may vary. Cheers