Mine are the same (6mm x 120mm) with OMF. There are a lot of wasps about at the moment, but they have learnt the hard way not to mess around near the entrance, both hives are very capable against wasps at the moment so they lurk underneath picking up scraps, but god help a bee that falls.
Today, it really looked like I should take the entrance block out all together as it being so warm, everyone was out and about and this size entrance was a real bottleneck, but is is staying put. Reducing the entrance at this time would give them more of a problem.
No mouse guards as they are still stacking in the pollen and our cats are extremely effective mousers.