Its-
As Donny has explained pretty well, you have to get the hands loaded in enough to get the inside out/circular handpath for good loading/connection/unloading ("circular handpath").
When you use a closed stance,it encourages doing this. A lot of people would be better off if they tried to "hide the hands" as opposed to getting at it indirectly by closing stance.
Similarly,when/if you open the stance, you really have to focus on hiding the hands to overcome the influence of the open stance.
OK, so now lets say you know how you need to move and position the hands and you also have an open stance. THEN the result is exactly the same as the way Epstein describes th shortening up of the swing for a 2 strike adjustment. In this case, you have to cover the whole plate, so you cam't look in or out,BUT you still have a good(but shorter/less separated) coil. The mental approach with this mechanical 2 strike adjustment that he finds works best is to look middle so you can still catch up to the inside stuff by keeping the hands in and turning on the ball (the old "Harry Heilman became a good htter when he learned to take the inside heater up the middle with 2 strikes thing) or let the ball get deep to adjust outside.
Epstein differed from Williams in how to make this adjustment.
Williams liked to "get more time" by closing the stance to set the contact points back, but Epstein doesn't like this becasue it makes the inside pitch hard to handle.
Epstein gets more time by rotating open to shorten the coil/load/swing while keeping sense of strike zone the same by keeping the spine/center the same distance from the plate. In addition.the axis is kept more upright which further levels out and shortens the swing by getting on top of the ball more.
Somewhat related to this is the (bogus for rotational power swing) idea of strding with the pitch. For a short quick swing such as the Aaron belly-up/quick hands, the foot will end up coming down somewhat more open for inside because you stop the hand cok sooner and start rotating sooner/well before front foot gets down which means the front foot comes down more open- see clips:
http://www.beabetterhitter.com/text/batspeed/coiling/coiling.htmThis is NOT the same as waiting to see where the ball is then desciding to stride that way- there is not enough time for that.
http://www.beabetterhitter.com/text/batspeed/coiling/coiling.htm