Hold the source power fixed and spread it over a larger area and the irradiance falls, since the same watts are shared across more square meters. This inverse relation E = P / A is a uniform-beam average, not a point-by-point profile. Real beams have non-uniform profiles and finite divergence, so the exact numbers hold only for the idealized spreading assumed here.
The same source power over a larger checked area gives a smaller irradiance. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
Same power over more area gives less irradiance
Both irradiance sources cite the same power before the comparison bit is accepted.