Lay your pen/rod across you fingers so you can grab it with the thumb on top with a relaxed grip and the pen is angled at about 65 degrees across a straight line down your forearm. Now lay the pen across and grab it with the three point grip. The angle decreases to about 20 degrees.
You can cock your wrist to get your pen/rod into alignment but this is a less "natural position" than the 3 point grip. Instructors use rubber bands, leather wrist straps, and even resort to putting the butt of the rod into the caster's sleeve just to try to force beginning fly casters into cocking that wrist forward during the backcast. They wouldn't have to do that if this was a natural way to get the proper rod to forearm allingment.
If the thumb on top aligned the rod with the forearm you wouldn't need this:
Stu's Fly Shop Individual Products - Outfitters - Top fly fishing gear.
And you wouldn't get these posts:
Wrist Break - how to cure it? - Fly Fishing Forums