Hi Brian, actually there is one other issue with that tail as well, which is that it isn't very good to try and fillet a very thin "knife edge" type situation like that.

You can see that the vertical section did fillet, but it did not produce a very good result in the back:





It is tough for the filleter to produce a nice corner in such a sharply angled "knife edge" situation like that.

If you want to fillet that well, it would probably be necessary to first fillet that very sharp edge so that it was a slightly rounded edge first (probably actually best to put a small rounded piece in there early on from the initial sweep actually), and then boolean the pieces together, then do a fillet where they met and it would then not have that "knife edge corner patch" type issue.

Filleting things that come to a very sharp angle generally can cause problems for MoI's filleter. You may have some better luck with those particular knife-edged ones in ViaCAD instead of MoI.

- Michael