i had the same problem with my trunk. i dont like firing port towards the cabin, because it seems to me that low end response isnt as good. i tried sub up, port back and it sounded great. idk how small an impreza trunk is, but with my car, i did 32w x 14.5h x 24d with a port that was 13h x 4w and 19 inches long, tuned to 35. left me with about 4 cubes after port displacement. crystal clear and hit lower than a mothafucka
Dude, that sounds almost ideal for my car. You wouldn't happen to have the specs & cut sheet would you?