mouseguard question

[Murox]

Which is fine and dandy until there's a flow on, bees need extra air circulation for honey ripening or undertaker bees need to clear out the dead - it is however a great retro fit when a hive is under relentless attack from wasps.

Yes it is a great retrofit. The handy feature is that you are free to make the actual entrance as wide or as narrow as you choose to accommodate population/usage increases when you build it. As BF pointed out the depth of the tunnel should not unduly interfere with airflow when fitted to an existing OMF. (perhaps it might be an issue if using solid floors?)