Knowing that you are a good golfer I expect you are not as consistent a shanker as you were with this swing or with the preset at club horizontal
Having a LOT of experience with the club horizontal preset myself it may be that the tension of the starting position is not relieved in the swing so the club face does not rotate to square. Since the IMA release depends more on mechanical connections than relaxation this is less of an issue with IMA though there is some (and that's part of the reason I created the 2.5 drill).
Peter