That's quite interesting.
I discovered the Merv 13's end up being my biggest bottle neck because they clog fast. I tried protecting my carbon shelves with their own dedicated Merv 13's, and it was just too hard on the airflow. My setup's problem is keeping things airtight within my cabinet. Still haven't totally solved that, so my prefilter isn't prefiltering everything. I'm now pretty eager for winter for once, where I can be a lot more lax about how much of my fumes make it outside. Here in Canada the smell of burning hardwood in the winter isn't a big problem