The supports & sky diffusers are optional on mine. However I use them all the time as the arms & top seen sideways give me a better frame of reference for shooting high enough to have a safety margin.
Avoid high mounted sights & scopes for testing as they'lll automatically put your LOS higher than your LOF, increasing the possibility of damage. If you must use a scope use the lowest power setting & you might see the screens through the scope.
Put a paper target a few inches behind the furthest screen with a 2~3" red target dot where you'd like the bullet to go & aim at the red dot.
Allan Quatermain: “Automatic rifles. Who in God's name has automatic rifles”?
Elderly Hunter: “That's dashed unsporting. Probably Belgium.”