There is another factor that can compromise effectiveness of bee passage through a queen excluder - too little space between the bottom of the honey super above and the next box. I used QE, in fact rely on them for optimal honey harvesting, and I had bought some plastic ones. I noticed that frames were being propolized to the top of the QE - then I pulled some frames from the super and just watched the traffic. Sure enough, bees could not pass under the super. The space was designed to have the gap of the hive below... once that is removed with a QE, not enough room.
I now use the wood-bound wire ones only. I think it is a shame the plastic ones are sold at all. I would wager they were developed and are sold exclusively by people who do not use them. Or by people who by chance did not have slightly shorter than expected honey super boxes.
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