Re-installing triple-track storm windows

I am trying to re-insert all the glass inserts of my storms. For winterproofing, does one insert go on the outermost track and the second one in the middle track, or do both go on the outermost track to provide a kind of seal?

Also, to help me save time in matching up all the panes I have to re-insert, are the two glass inserts per window the same size, or is one larger than the other? It sort of looks like one is slight larger in order to fit in the middle track, while the smaller one fits the outer track. This would make sense if you use two tracks (outer and middle) for winterproofing.

Thanks in advance.