According to the 2007 Subaru Impreza Shop Manual you should hand tighten 1 rotation past where the seal meets the block, then using a filter wrench tighten another 2/3 - 3/4 rotation.
5) Install the oil filter by turning it by hand, being
careful not to damage seal rubber.
***8226; Tighten the oil filter 68 mm (2.68 in) in diameter
(approx. 1 rotation) after the seal rubber of the oil
filter comes in contact with cylinder block or oil
cooler. Use the 14 N·m (1.4 kgf-m, 10.3 ft-lb)
torque, if the torque wrench is available.
***8226; Tighten the oil filter with 65 mm (2.56 in) in diameter
further (approx. 2/3 - 3/4 rotations) after the
seal rubber of the oil filter comes in contact with cylinder
block or oil cooler. Use the 12 N·m (1.2 kgf-m,
8.7 ft-lb) torque, if the torque wrench is available.
In other words, if you are just going hand tight you are not getting the filter tight enough.