Andrei, thanks for the video. I think I tried this approach earlier on, but I wasn't getting good results. The difference was that I was trimming away a larger portion of the surface before blending. The trim I made was a segment all the way through the back of this solid. When I blended, I got some lumpiness on the back where the flat plane blended with the top. Your trim yielded a better blend, although I wasn't able to join the resulting surfaces into a solid. I made an adjusted trim line and blended that, and I was finally able to get a solid in about 30 seconds of work. This piece has been a headache, but I've learned a lot!

Brandroid I did not understand you, you could not join model using my method? I joined it in video and made solid everythink was ok)

ANdrei,
In your video, you did not trim the top surface "all the way back"... You started at the back seam edge.

When he trimmed it all the way back, he was having issues.

The 2 surfaces at the back (converging area) are not really tangent, or equal, so the blend back there is producing the poor results.

He fixed it by trimming out a larger portion of the top, AND bottom. That is kindof "hiding" the stressed surface.

The best thing would be to re-create that object, and have the back "converged" area come from "one initial piece". Either the bottom piece, or the top piece. One or the other.

BurrMan is right, although initially I replicated everything Andrei did in his video. My first trim line was the same as his, and still I could not get a solid after blending the resulting surfaces; only a joined surface.

Then I cut through entire piece above and below the lip and got an acceptable result.

Hello,

The back edges of the original model are not fitting too well, rebuilding the base model from scratch leaves a better end result.

Good, understood.
I made new tutorial about Collapsing fillet (disappearing fillet). You can check it here:
http://moi3d.com/forum/index.php?webtag=MOI&msg=6058.30