Proper filter for Trane Perfect Fit TFM215B0AH0
I have a 21" Trane Perfect Fit Air Cleaner, model TFM215B0AH0. I purchased a replacement TRANE 5" media filter, part BAYFTAH21M, for it a few months ago. I went to replace the filter last week and realized that my unit has the Retrofit Frame Kit with the 5" expandable filter (BAYFTAHEXM) installed. The frame kit is about 1" higher than the BAYFTAH21M filter and seems to fit nicely in the unit.
Is the BAYFTAH21M filter compatible with this unit? I'm curious because there is a 1"+ gap between the top of the filter and the top of the PerfectFit unit. Should it fit fairly snug? Just want to confirm before I go out and purchase the expandable filters.
Thanks for your time and assistance.