Some of the guys that do offensive dynasty rankings subscribe to some complicated theories of three and four year windows, decreasing percentages of expected production as you suggested.On the IDP side, I'm a big believer that your dynasty philosophy is made simple by the impact that a coaching or scheme change or new surrounding cast (single FA acquisition or loss, etc) has on the value of an IDP.1. Get studs that are (presumably) matchup, scheme and surrounding cast independent and hold them until they fall apart.2. Fill in with slightly above replacement level talent who appear to be in the best situation in the coming season.3. Roster players with big talent who could enter category 1 when they finally get their chance.Otherwise, replacement level players -- those around the 30-50 slots in the ranking each season with no top 15 upside -- are just that, replaceable. Be prepared to shuffle those roster slots every year. The extent to which you'll have to do that depends on how many category 1 and 3 players you have (and can get) rostered.So, my dynasty rankings usually have a 1 - 1.5 year window. I don't care much what the future holds, because it's difficult to predict. The studs with what looks to be little chance to go in the tank sit in the top tiers, the good players with a few question marks fall in the middle tiers ranked by upside and the borderline starter tiers are a mix of big upside without opportunity (yet) and the replacement level talent who look unlikely to see their situation change for the worse next season.But, yes, the players find themselves in tiers to begin with based on loose projections of solos, total tackles and big plays (sacks and coverage). For me, everything works from a full season solo tackle projection to generate the rough tiers. Big play guys get bumped up, guys who can't make big plays or have questionable talent or who are situation/scheme dependent get bumped down a bit.As much as we try to make it a scientific process based on stats and rate stats based off of the stats, there's still a fair amount of gut feel involved due to the nature of defensive football.