Hi Tony, so I took a bit closer look and basically that little bowed out area that I showed previously is where the vertical pieces kind of stick out like a little tiny shelf instead of being all the way submerged in the upper piece.

So that little portion sticking out is what's making things more complex here.

I've attached an edited version of the model where I pulled in 2 control points of those vertical pieces so that they didn't stick out with that little tiny shelf-like spot and that seems to make it work a lot better. This version you should be able to fillet up to a radius of about 0.1, much larger than that and these pieces will start running into each other:



- Michael