I think it works a bit different . They aren't keeping the DR = armor/(armor + 300) equation for enemy armor anymore. They will be implementing a new equation that spreads it out more evenly but only on enemies. They will also be increasing the minimum armors to reflect the change so that lower level enemies don't get like 3% DR.
As of yet they haven't given information on the new equation and they probably aren't done working it out yet.
"The Armor scaling curve will aim to be a bit more spread out, as opposed to being bottom-heavy. Partial strip from the top end will allow for more consistent damage gains, as opposed to needing to have a total Armor Strip."
Although they did say 2,700 and I don't see how you'd get that to still work out to 90% using a different equation but that might have just been said because they still haven't worked it out yet and don't have the final defense number after implementing the new system. They just know they want a 90% DR from defense cap.