One thing I observed in Joe Root's batting in SL series is that he has changed his technique against fast bowlers at least. Previously he used to have the straight back trigger movement which kept him closed off after the trigger. But in the SL series, I see he is moving the back leg back and across with front foot almost at same place as original, similar to Steve Smith and this ending up in a open position similar to Gary Palmer technique. Not sure if this minor change is the reason for his new found form or if this is just a temporary adjustment he made only for the subcontinent.