Quote: my plane was far more upright even though I thought I was still swinging correctly
This is exactly the problem with the explanar. If you consider the plane of your downswing, on a good swing, you will notice that the butt end of the club points directly at the ball as the club drops onto plane. BUT, if you swing it back like this (as I did) any pro will most likely say you are swinging very flat. Most methods (especially Leadbetter) like to see a marginally upright plane on the backswing and then re-route the club "into the slot" on the downswing. I spent 2 months setting the club inside the ball at 9 o'clock (where the butt end points) and every lesson he wants it more upright still. Explanar encourages a one plane swing....which is great....to an extent.
I'll try to find some photos to show the two plane method my pro is looking for.