Here is a picture of the corner where I want to create a setback fillet.  It doesn't seem to work because the bottom edge is too short and turns into the curve.

I created a spline that very nearly matches the shape of my desired geometry, and in this case it works, I think because it is a continuous line.

Is there a way to achieve this with the real geometry that I want, or am I stuck with this workaround?

Thanks!