Just tossing out ideas here but...
What would be people's thoughts on having each scenario in an AoS event - escalate the narrative conflict.
Like:
Game 1 - 20-35 models ( or wounds whatever mechanic we use)
Game 2 - 30-50 models
Game 3 - 40-60
etc...
As each game goes really fast - like a 20-35 model game is generally over in 45 minutes, etc..
Just tossing out feelers here, nothing set in stone.
Spit-balling if you will.