At this point maybe Ames, DCG, Norwalk and Indianola need to join the CIML and split the league up into two divisions by size. Something like this, though they might want to play around with it based on economic multipliers, success factors, etc:
Large:
Valley, Johnston, Waukee, Waukee NW, Centennial, SEP, Ankeny
Small:
Dowling, New Waukee HS, Ames, Urbandale, DCG, Norwalk, Indianola
It seems like there are some good solutions to the larger central Iowa schools. I'd like to see something like the above, and as far as the metros, have them stay with FD, Marshalltown, and Ottumwa to make an 8 team league, maybe get Newton in there.
Then in a few years I could see B-F and NP getting big enough to join the smaller school division of the CIML and bump up Dowling and the new Waukee school, for example.
I don't think in Central Iowa among the 3A-5A schools conference size is that important. An AD might disagree, but it seems like non-con scheduling opportunities are plentiful.