I've been trying to build a section where the player travels up a thin tower in a tractor beam while coming under turret fire from the top of the tower. I experimented with trying to hold the turret in place at a 90 degree angle for a while, but I couldn't seem to make it work. So I've instead tried placing the turret down normally with a prop_portal in front of it and a matching portal looking down the tower.

It all seems to work, except the turret is quite amazingly poor at target finding through the portal. It'll shoot at me if I'm like a meter below the portal, but no further, even when I'm so directly below it that the turret's laser is painting my head. The tower is about 1300 units deep and the turret's range is set to ~2000 units.

Does anyone have any ideas or might I be out of luck?
Sorry for the long post.