BTW Don, I have worked slightly on using a Kirk Junge approach to single plane Set Up for Impact. It seems to get me slightly steeper and then the Sterling sole design seems to work better maybe that was Tom Wishon's intention in the design not sure.
To work on this more I need to change the shaft in my Sterling 5i, 7i, 9i, PW and SW test irons find a good playing length/lie and correlation and grip size for Junge's Set Up for Impact which for me is much different than SL double plane.
IMO single plane is the way to play to really take advantage of SL.