The filter was actually only about 3 1/2 inches deep so air is going to go through the path of least resistance whicih is going around the filter. The filter description said it was 4 inches but it is not. Your concept is a good one but you need to have quality filters.
I was so glad to find a filter made in the USA. Its good quality, just ever so slightly smaller than my old one. It fits, though and should do the job.
At this time I don't really have a rating of the filters other than I was told these are the best air filters. Ask me again in about 3 months and I should have a better idea of the product.Thanks,God Bless!!Arthur Glover Sr.