[Worknplay9]

Smooth,
I had the same problem; pulling the short irons only. Turns out that I was bending the left wrist at impact (ok, the problem that most ams have). This after a year of working hard on FLW and BRW. But, in my case (and maybe yours) it was because the short irons are the heaviest, and therefore the breakdown becomes "easier". Also, (again in my case) because we think "it's just a wedge" we sometimes don't finish the swing, and quit. What finally worked wonders for me was to make sure I finished the swing, along with a determined roll of the left forearm, a horizontal hinge.
Tom