On the “half,” are you rounding up or down? This makes a bit of a difference, since it includes the bootee.
Can you be more specific about the minimum level? Limiting AO3 games to 45-50 doesn't actually solve the problem for me. What annoys me most is when a game is filled with 47-49 power levelers who all leave before the boss. I feel like I just wasted my time doing the map at all. If I'm after the boss, I only want to do these runs with level 50s.
Yes, this is really annoying to lower level players trying to open maps. Sorry, but there's a social problem in this game that needs to be solved better. One way might be to introduce serious incentives to get people to finish maps. A suggestion I had a while back was to make certain things (kills? prizes?) only accrue to the players when the map is finished.
For the lower level dungeons, I would also really like a maximum level option.