[EdZ]

Try checking plane using a flashlight rather than a dowel.

Get two small mag lights and tape them end to end.

You can focus the beams down to a fairly small circle. This with give you a better idea if you are tracing the plane going back because it shows you where PP#3 is tracing.

As a guess without seeing your motion, you are either extremely flat going back (shoulder turn takeaway) and/or you are letting your hands move 'out' and over swiveling/turning going back, right off the ball.

Some other drills for you -

practice your backswing very slowly with your back near a wall (use a wedge, stand slightly away from the wall)

Have someone hold a club/dowel parallel to your targetline just in front of your hands at address and take a backswing. Keep the clubhead outside that shaft/dowel until near hip high.

To get the feel for keeping the clubhead 'out in front' of you, do some split grip drills/takeaways. If you have been really taking it in/over swiveling, you should get a feel that you are getting your hands 'under' the shaft - almost an early wrist set 'feel' - from there you can get the club UP plane