that's actually a trick question. You should aim the same way for both. Pythagoras's theorum explains why you'll probably shoot over the make, either up or down hill.
Usually a common rifle is considered "grounded" as fire line [so accurate] within an angle of 30° with the target. When you go hunting on mountain it may happen that a pray is not at your level and the angle that the rifle has to reach to shoot is superior than +30° [or -30°], in any case, personally I tend to consider an inclination of 20° already well "sensitive" [using a common rifle]. When you incline your rifle the principal of the rotation of the trajectory can even make you miss the target. When you shoot uphill the bullet will follow a trajectory which will make it fall before of the target you are aiming to, so that you have to make it follow a higher trajectory [so you aim over]. When you shoot downhill the bullet will tend to fall after the target [it's the same when a skier jumps from a trampoline, he takes land well far simply because he jumps downhill, if he would have to jump uphill ...], so that you have to aim under the target. Take a look at this picture: Substantially the points A' [the one uphill and the one downhill] are the points where the bullet will fall. You can see that A' is more near when you shoot uphill and more far when you shoot downhill. This if you leave the bullet fall because of gravity, but it's the same if you have to hit a far target, you have to consider this effect [in the drawing the points A indicate where your targets are].
