Short answer: The field of view is 60° horizontally and 45° vertically.
Coverage grows linearly because the field of view is a fixed cone: each additional meter of slope distance increases the horizontal span by ~1.155 m (measured from the camera pinhole). At maximum range, we expect a half span of ±40.41 m (80.83 m full span).
Vertically, the span increases by ~0.828 m per meter of slope distance (because the vertical field of view is narrower). At full range (70 m), we expect a half span of ±28.99 m and a full span of ~58 m.