While trying to use a big two mesh filter on wort going into my primary fermentor I had issues with the 10" funnel not staying put. I just couldn't trust it to not tip over, again. I tried wrapping the junction between funnel and carboy with multiple layers of aluminum foil which sort of worked.
Then I got a new 1" ID blow-off tube that was too long, and cut 6" off of it. I tried putting the funnel into the short tube and found that I could get it to go in over an inch when it was warm and I could stick the other end into the carboy with no problem.
There is a finite distance that the funnel can be pushed into the blow off tube and if you have too much tube outside the carboy the funnel moves around. Too much tube in the carboy might not be fun to pull out. It turns out that you only need it to be 3-4" long to stabilize the funnel hands free.
Hope this helps!