Alien Vs Predator - 30 Degrees Is Not Straight Down
When they first see the abandoned whaling station, the chick says that the pyramid is 2000ft directly below, however, the tunnel is at a 30 degree angle to the ground starting at the station.
2000ft = ~700m (I'm Australian - Metric)
700 / Tan 30 = 1212.5m
That means the pyramid is actually 1200m away from the station.
You can also see this in the thermal picture that Bishop Weyland Shows them of the tunnel.