I practice in my backyard a lot too. 90% of the time, I just shoot from the ground anywhere from 20 to 30 yards. I have taken a ladder and climbed up on my back porch roof and shot a few arrows from that vantage point.

Remember high school algebra and geometry? Remember the "Pythagorum theory" (sp)? {Remember A2 + B2 = C2?} Well, it is true.... The sights will be slightly off when shooting from 15 feet up on a roof, versus shooting from ground level.

Distance: 30 yards/90 feet {A2 = 8100}
Height: 15 feet {B2 = 225}
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Hypoteneuse: 91.24 feet/30.41 yards {C2 = 8325}

Butch A.