RF is a funny animal. As a student of the propagation both practical and philosophical, that is a hard question to answer.
There are a lot of assumptions about RF…the electro magnetic kind. About longer and short frequencies and attenuation, quarter wave lengths, whether or not metals reflect RF or is it absorbed and re broadcast. If RF CAN 'bend' around corners without being 'physically' effected by an object…the way it can rise and fall according to a geographical geologic dybamic….the way you see a flick of birds travel together low on the ground.
In practical terms, LOS is the most effective way to get a clean return. Coupled with any flat obstacles like walks be penetrated as close to perpendicularly as possible.
If not a 6 inch wall can look like a 7 foot thick wall when penetration occurs at acute or obtuse angles.
Or you can just buy repeaters an extenders, etc