Coverage is a shape, not a circle
Three effects stack to make the real coverage curve. Free-space path loss grows as 20·log10(distance) + 20·log10(frequency), so before anything else a 6 GHz link starts several dB behind 2.4 GHz at the same range. The two-ray ground-reflection model adds a floor-bounced ray whose phase difference with the direct ray (set by the wavelength) creates constructive peaks and deep fading nulls — the ripples you see as you move. Material loss compounds on top and rises with frequency.
This lab makes all three tangible: choose a band, add a wall material, and slide a receiver along an RSSI-vs-distance plot drawn from the actual model, with a side-view of the direct and reflected rays and the Fresnel zone. It's the intuition behind every survey — pick the band for the job, design to a margin above threshold, and never trust 'good bars' at a single spot, because multipath guarantees a null is nearby.