Just use some screen wire, plastic or metal. Add it to the end of your cone by wraping it around the current end. Tape the extended cone to the end of the first cone. The longer you make the entension the less likely they will ever get back in through the cone.
Once you have that fixed then you will be able to see where the real "holes" are in your setup. Trust me, I have never gotten one to work on the first try. Most of my trapouts take 5 or 6 attempts before I finally get it where bees cannot get back into their hive (tree, bldg, etc.). Bees are very persistant.
I can't tell you how many times I was sure I had all bases covered only to be skunked by bees. :scratch: