Hi Mir4ea, yes the problem in your case here is this little tiny edge that is a side effect of having the cone slightly off center:



The edge-based filleter has a limitation that it will only be able to construct a fillet that partially eats away that edge, it won't be able to totally consume it away. And because the edge is quite small that basically puts a small limit on the size of the fillet radius that can be used here.

It is possible to place a fillet onto your original model there using the surface/surface filleting mechanism instead though - if you use Edit > Separate on your model to break it into individual surface, and then select 2 surfaces and do a fillet the filleter does a somewhat different surface/surface type fillet generation which is created just between surface data rather than tracking along edges like the regular edge-based filleter. It can generate fillets in cases where the edge-based one gets confused, but unlike the edge based one it does not know how to handle junctures where multiple fillets are coming together, you just basically get some fillet surfaces that you may need to trim yourself.

But basically in general it's not good for filleting to have little tiny edge pieces, that can cause various problems with the edge-based filleting.

- Michael