Forward is up. Green arcs on the deck rim are openings, and the brown petals show where escaping stones go (longer = more). A stone hit at angle φ meets the rim about 32° further round. Through the front gap it leaves at the tangent, but only ~30% fit under the raised skirt (75% when tipped up). Through a tunnel or chute it leaves in the chute's direction. A bag catches 90%. The numbers are a first pass, to be tuned in the sandbox.