I took a look at the Store tab in Impulse and tried sorting some items.  For instance, under Games, if I sort the default "Tile" view by Popularity with no filter, I get a two column scrollable display.  But, there's no indication of whether the Tiles are sorted vertically first or horizontally.  Since the display is scrollable, I would have assumed the sort order was primarily horizontal, otherwise I'd have to scroll to the bottom, then the top, then the bottom again to go through the list in order.  So, I changed the view from "Tile" to "Detailed."  Oopsie!  Looks like I was wrong.  The primary sort order is vertical.  Assuming you want to keep a dual column "Tile" display, I'd recommend adding numbers so that people can tell how the order progresses.

One other thing.  I'm not sure that the icon used in the list boxes is correct.  Each of the View As, Sort By, and Filter list boxes has a little double-ended up-and-down arrow-head next to it.  To me, this implies that clicking on one or the other arrow will cause the list to scroll through its options.  Instead, the two arrow-heads are actually one icon and clicking on it opens the list box from which I can choose an option.  Some other icon, like the standard(?) single-down-arrow might be better.