So does the top vents stop heat rising?
No, it won't stop warm air convecting, but sure as 'eggs is eggs', it wont stay where you want it! The average temperature at the top of the hive will be lower as there will be more dilution air.
One might wonder why Vita have done trials on hundreds of hives and given an average efficacy of 93%(?), but none recorded as done in the UK (well, not that are shown in those statistics, anyway)?
Makes me wonder whether any UK test results (and others possibly) have been 'conveniently' omitted because they would drag down the overall average?
Anyone suggesting consistently over 90% for autumn apiguard treatment in the UK is being over-optimistic in my opinion, and certainly not corroborated by Vita on their website - well not that I have seen, or remembered seeing.
When I note a warning for half a dose on half a hive, but no warning of a full dose on a full hive (exactly the same ratio of dose to box size), I get more suspicious of marketing/advertising hype than usual.