how big that pool actually lands.
D = 2d·tan(θ/2) · E = cd/d² — the math every throw distance argument ends with.
punch in a beam angle and a throw distance, get the pool diameter on stage. field angle runs alongside it, with presets for the usual 19°, 26°, 36° and 50° profiles and mover zooms. add a candela figure and it gives center illuminance.
the math is D = 2d · tan(θ/2). beam angle is where intensity drops to 50% of center, field angle is 10% — which is why field is the bigger number, and why the edge of the pool looks softer than the spec sheet implies.
space a wash off the field diameter, overlapping about 70%. what you measure on the deck is nearly always field, not beam — check which one the manual quotes before you argue about it at focus.