FilletSrf can we have a chain and trim with it?

Hi,
FilletEdge failed here,
so try FilletSrf

either Extend On and trim on, or extend off and trim on, results need further work to trim away the surfaces.

If FilletEdge works then all is done and we move on.

try it again and now it works,…gremlins !

and enemies of FilletEdge will say told you so.

and why cannot there be a filletSrf allowing me to make my way round this shape then it finishes the command and trims ?

At the moment I have to trim the 8 upright surfaces with the result, then trim a firther gap in the base item.

How do other CAD progs fare on such ?
Fillet method.3dm (647.1 KB)

Steve