WARNING: This page is about a different car, the 2005 Subaru Outback and 2005 Subaru Legacy. However, it is still accessible from the selected car via links, so may be relevant.
During shifting, the line pressure is set to a level suitable for the input speed, input torque and the difference between the required and current gear speed.
Fig 1: Identifying Graph (Line-Pressure Control During Shifting)