Very good discussion of shooting at targets above and below you in "Timeless Bowhunting," by Roy Marlow. In short, there's a tendency to shoot too high whether the target is above or below you for a number of reasons. The animals look farther away than they are. The horizontal distance to the target is less than the angled distance and thus gravity has less time to work on the arrow, etc. A sight shooter would shoot the horizontal distance to the animal, not the vertical. So if the animal was 5 meters out and 20 meters down, the sight shooter would shoot the animal as if it were 5 meters away. To answer your question, yes, you would pretty much be holding dead on. Remember to bend at the waist though to keep your draw length from shortening. But don't wait until you have a tahr standing under you. Try to practice that shot now, you lucky devil.