I read this thread with great interest as I've struggled getting the club to "lay on the line" for years. Lynn and I have worked quite a bit on this, and during our school at Pine Tree last week, another contributor to being "under plane" in startup/backstroke came into view.
The golfer can have EA, minimal pivot (acquired motion) and still have trouble maintaining the clubshaft's alignment to the plane line; wrist conditions (Mechanical Checklist, Section 4/5, #16) also play a role. Remember the left wrist cock is a vertical motion. Go to impact fix - then cock the left wrist vertically. This gives you the wrist alignments at top (and at finish)
I found my left wrist arched as I moved from startup into backstroke. This caused the need for a compensating move at top. Life got much simpler lately when I corrected this error.
Moral to the story: Use 12-3 Mechanical checklist. The answers are there!
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