Hi Peter, and actually probably the easiest way to finish the fillet is to export to a different CAD program that handles that kind of case better than MoI, do it there and then import the file back again.

A couple of programs that can help with that are Autodesk 123D (free: http://www.123dapp.com/123d) or ViaCAD ($99 http://www.punchcad.com/p-9-viacad-2d3d-v8.aspx).

What you'd probably want to do is have the initial shape have all sharp corners initially, like this (also see attached 3DM model file):



Then bring that in to 123D or ViaCAD and do the fillet there along the entire sharp edges - unfortunately this particular case just flat out does not work very well in MoI currently, and using a separate tool for doing it is likely to be the easiest method.

Hopefully more cases like this will work in the future as the people who make the geometry library that MoI uses continue to tune it up. This particular "disappearing fillet" case comes up fairly often so I will ask them about it specifically.

- Michael