I'd say side to side more than anything else. I'm gonna go skiing right now so I'll pay close attention and edit this post with more info.

About a month ago I sized down my Lange RX 130 pros so that I now have a ~1cm shell fit. They worked great out of the box for about 15 days but are now feeling sloppy and I imagine the problem is...

I sized down in the RX130 as well. According to the Lange chart they had in the back of the shop I should be in a 27.5 (both feet were around 274mm) but I sized down to a 26.5 and have a 1cm shell...