Hi Marco, so you'd want to do it more like this - starting with the main object which is already extended as far as you need (so no "tacking on" needed), do the fillets in order of largest to smallest, so starting with this one:





Then next these:





Then select the whole model and do the smallest radius:



Don't try to simulate a fillet by filling in areas with Network, just in general you want to be working more by carving away pieces rather than filling in pieces patch by patch.

- Michael