OK, thought I would create a top entrance for the bees for easy access to the supers (and also for additional ventilation). Now I thought I read where it's posible to simply modify the inner cover by removing a section of the inner cover shim, so I used a router and now a one-inch section of the shim is gone. I put it back on top of the super with the opening side down. The telescoping cover is loose enough that allows a small gap so that bees should be able to use the new entrance.
The problem is the bees would rather propolize this entrance closed. What is wrong?