If you did your research BTW for which there was a very insightful article from seekingalpha on after day performance over the past 3 years every quarter (so 12 quarters)
So why would it go down as much as you expect tomorrow?
Look at March 2011 when it went up 8% more than it's after hours price.
"On March 23, 2011, RHT soared 10% in after-hours action after beating Q4 estimates and setting its guidance above the Street view. The stock surged even higher the next day, closing the March 24 regular session up 18.2%."