the 3M "purple" filter which I think is MERV 11 has something like 3 pleats per inch, while the MERV 7 has only 1 pleat per inch. But the MERV 11 filter has a much more restrictive filter material.
Why would you expect all different MERV filters to have the same pressure drop? or to have the pressure drop increase with MERV ratings. You have to consider the pressure dorp of a "1" square of their filter material, then know the total surface area of material used. So the MERV 11 might have 3X the pressure dorp of the MERV 7, but has 3.5X the total surface area, so it has a lower overall pressure drop.