You've now got that head hummin' right along, but as a function of your body's design and weight, your ability to continue accelerating the mass at this point is sorely limited.   In order to remedy this situation we have to get sneaky.  In large part, to this place, the force on the hammer has been a massive downward jerk, but that is about to change.  Fig.4 illustrates a straightening of the right arm continuing to apply downward force, while the left hand suddenly and briskly applies upward force at the end of the handle.  With the right arm locked and the left hand pulling upward, the right hand functions as a fulcrum, the left hand as a force applied to an unequal length lever, and by golly, that puts the head on the fast end of the lever.  That is, with 1" of movement of the left hand, something along the lines of 20" of head movement can be produced.  At the  beginning of the stroke this would produce glacial acceleration, but once you're moving it's like being able to shift to a higher bicycle gear after you've built up some speed.  Happily, this upward shift begins lifting the body to facilitate the recovery phase of the swing from a somewhat bent posture.  Hopefully this has all resulted in an astonishing snap at the end of the swing, slapping the workpiece so energetically into the anvil that the rebound has carried the head back up almost chest high, a position from which it can almost effortlessly be snatched and cocked behind the right ear without having to reel it in and lift it with muscle power.  I get lucky maybe once every third stroke with a freebie, but I'll take what I can get.  On recovery, the right hand should be slid up to the head while the left pulls rearward, from there it's just a matter of lifting the hammer into the cocked position.  If you get one of those chest high bounces, you're in "catch as catch can" territory, and any way you  can reel it in while maintaining efficiency and not doing any one or any thing harm is just fine.