Obstructions have no special relevance to the asymmetry of power output between communication devices -- because they attenuate signal similarly for both devices. If you have good signal one way, you should also have good signal the other way, obstruction or not.
Lest we go too far into the weeds, the point in question is how a tiny phone transmitter achieves the same distance as the huge cell tower antennae with hundreds of watts at its disposal - before we take interference into consideration (which acts as a limit on this asymmetry).
All RF receivers need an amplifier, and the one in the phone is restricted by its power budget unlike the ones on the cell tower. This is part of the asymmetry, which is not about transmission power alone.
In this analogy, the speaker on the stage holding the microphone has extremely sharp hearing, so that she can listen to any one of the audience without also giving them a microphone, and thus hold a conversation with them.
But while she can still hear people speaking from outside the meeting hall with her super hearing, she has trouble distinguishing the sounds because there is construction going on in the hallway.