Hmmm. I wonder if you are talking about the angle of the bottom of the ski to the ice instead of the skis to each other? I set mine flat but now you got me thinking. If the skis rode on one edge on ice they would pull easier, and it shouldn't affect how they ride on snow.
I think a more important factor is to try and get the skis to be flat all along their length once your setup is loaded. The skis I used on my Smitty had a pronounced rocker and would only contact the ice at the front and rear. So I straightened them out with an extra piece of wood between the uprights. Made a pronounced difference.