winterizing migratory hives

[jxbeeman]

my question is about different ways to winterize the migratory style hive.  i've just started using MH tops.  to winterize the hives that are using the telescoping cover i always had a knotch cut out on one side of the inner cover to allow airflow and ventilation.  in the summer time i usually flip it knotch up and in the winter time i flip it to knotch down.  
so i guess the question is for the migratory covers do you need like an upper entrance or do you just not bother with it.  i've talked to one guy and what he does is to slide the top hb back one beespace and that is what he does to winterize them.

so any methods of winterization would be appriciated.

http://pg.photos.yahoo.com/ph/josh_bestle/detail?.dir=2e5a&.dnm=77ef.jpg&.src=ph

[Michael Bush]

You still need an upper entrance for all the reasons you already needed one.  Snow, dead bees, condensation.  Except with a migratory there's even more condensation.  I prop mine up with shingle shims to make a top entnrace already, so I just reduce the entrance with another piece of wood and put some styrofoam on top to cut down on condensation.  Of course, the warmer your climate the less necessary all this becomes.