i have no experience with using top entrance only but...i've seen quite a few bees pulling a large load so...i guess they will just drag them up instead of forward. anyway they try to drag/fly the dead bees as far away from the hive as possible. i once focused on one bee (actually 2) and it was easyer since it was quite a big dot, and i saw her fly at least 50 meters and at least 20 in the air. so don't worry. plus, like you said it, most die outside.