Like wot MikeB says, RF propagation follows simple, clearly-defined rules. I passed the theory exams in those when I was a nipper.
The trouble is, when you get up into frequencies in Gigahertz (like WiFi), the interactions that affect that propagation become incredibly complex. This is the point where you wave the aerial around a bit and enquire of the parentage of the inventor.
I can squirt RF all round the globe (and have done, frequently) - but there are a load of conditions that need to apply. Hardly any of those apply to WiFi. With WiFi, I work on the simple principle that it will percolate through about 50m of free air, or one stone wall, or two stud walls, or two glass windows (as long as the glass isn't metallised) - or any combination thereof pro-rata.
If you are lucky and the humidity is right and the electrons didn't get stoned last night, you may get some random better results than that. But that's not the way to bet.