I have a regency I3100L model insert. I changed the side firebricks today in anticipation of burning season, but also seem to have two large firebricks along the ceiling of the insert, sitting right above 4 venting tubes. They are ~11x11 and seem a little thinner than the side standard firebricks, but can't seem to search properly to find / buy replacements. Any help on what these are or where I can find replacements? Thanks so much!