Yes fixed pins on the ground will shoot high from a tree or stand.
Not too bad with todays high speed bows but there is a difference. it happens with rifles too, shooting down a mountain. Let me see if I can explain it. If your shooting straight out from the ground, gravity is pulling down on your arrow or bullet giving it that arch, the farther away you are the greater this arch becomes. Now when your shooting down from a tree or mountain gravity no longer has this affect because your already shootin down, so no arch is created, the bullet or arrow is flying with a perfect straight trajectory. So when you sight your bow in on the ground at 30 yds your actually aiming high to get the arrow to hit the bull because of the arch, now when you get up in stand and shoot down at a target thats 30 yds out and down your arrow will hit high if you use that same 30 yd pin. Now it's not much with todays bows but it still will hit high, the farther and higher you are the greater this becomes.