Dragon God HELP!

[ChaosOrigin]

So in facing the Dragon God, I managed to hit him with both anti-dragon weapons and make his head hang low enough for me to finish his small amount of health off. But here's the problem: I CAN'T HIT CAUSE DAMAGE NO MATTER WHERE I STAND! I stand on every possible angle on that ledge, but his head takes no damage regardless, it just continues to move back and forth, half of it vanishing into the rock.

Am I facing a glitch that stops me from defeating the Arch demon!? Or is there just something I'm missing? Please, enlighten me!

[Myrkan]

Attack the white horn.

[HijiriOni]

It's on his Chin.

Also DO NOT melee it, currently there is a bug that if you melee it, he may kill you at the same moment you kill him, and if this happens it registers him as dead but bugs your game so you cannot advance. You also won't get the trophy for beating him.