Something like a sequence more like this (see attached 3DM file also):



The last steps are putting in a large radius fillet here first:



Then a smaller radius fillet here:



So you've got to kind of build things in more stages and sub components than what you've been trying, and the smaller rounded areas
have to wait until the end until the larger fillets have been done first.

But these can also be some pretty difficult fillets for MoI to calculate as well, this has one of those "surfaces meet smoothly" type
situations in it where you can see the last fillet shrinks down to a point. When it's just a point at the very end of the fillet it can be
more feasible though. You may need some assistance from another CAD program with more robust fillets in it though for
this type of multiple level filleting.

Hope this helps give you more of the idea of how things are blocked out into separate pieces to start with though.

- Michael