Networks cannot give an average unless it`s for a fixed CPM, Percentage based CPM rates give you a percentage of whatever ad revenue is generated off your videos , it depends on so many factors that if a network can give you an average they have no idea about their own payments :|
Also it is helpful to note that Networks that sell their own ads Maker , Fullscreen , BentPixels etc then the CPMs will be higher and it`s also good to note that CPMs can be really high if the network has special offers : Fullscreen (Gorilla Program) , Vultra (Promotions) etc