Hi Chipp, in the attached 3DM file that little zone shown above has been reworked to cut out that little slivery shelf and now that edge should fillet ok for you.
I trimmed off the sliver with an extended line and then also had to trim the side wall on the opposite side from that so that it was all trued up and that area was one single large plane, this one here:
I really appreciate you taking the time to explain this. Examples like the one you show are clear and easily reproducible and gives me confidence there is always a solution. Much thanks!