To be honest my ideal preference is a national primary day, and as I say if need be repeat the primary multiple times (so primaries monthly every month from February to June, each worth 20% of the delegates)
What makes you think though that each month things would go differently? especially considering that likely those candidates who went badly in the first round might simply drop out?
Precisely that candidates that did badly would drop out is what would change things
Not to mention candidates that did surprisingly well getting a boost and what not.