A3. Most microplate methods have edge effects but we have found these to be fairly minimal. To overcome this or minimise the effects, you could randomise your block design but if you get very large variation which has nothing to do with the seal, it is likely to be due to unequal heat distribution across the plate.
There are incubators on the market that are specific for incubating microplates with very good air circulation, and have a large area available so plates are not stacked. It is good practice to check temperature control and variation in your incubator and as a compromise try not stacking too many plates together (e.g. < 3).