I'm speaking from an end user, not a designer perspective. Yes, I was using caving as the extreme indicator. Office buildings and the average user location have nowhere near the resistance to transmission signals as a cave. In larger buildings, like malls and high rises, blocking and interference with transmission signals is a known issue. On 9/11, one of the reasons so many firefighters were killed was because radio transmissions inside the WTC were not received due to building interference. A mayday was called, but many firefighters did not receive the transmission. Of course, the massive overload in all transmission channels from cell phones, television remote units, fire, ems, police and state and federal agencies also contributed. Most modern fire codes now include provisions requiring buildings exceeding a specific size to install internal building repeaters that mimic the tower repeaters located around the municipality for emergency services.
In cave rescue, transmission issues underground have been known for a long time. I am not aware of any receiving device that will work wirelessly in a cave. The issue starts as soon as you are deep enough in the cave that you lose line of sight with the exterior, although transmission may extend a little deeper in solid rock caves where transmissions will extend a little deeper as transmissions bounce, but are usually not good for more than twenty feet inside a cave. Our solution was to use an old army line wire radio with about a mile of wire and the handsets that would clamp onto the wire at any location to make a connection. The wire was on a spool, and the insulation was self healing so you didn't damage it when you attached the hand set.
If you know of a method of actually transmitting through rock, freep mail me. We can be millionaires.
As to our original discussion, I understand that we're talking about a guppy and a whale when talking about the differences between covering an antenna with your hand and transmitting inside a cave, but your response was extremely interesting, and ran me off on this tangent.
i need a couple of minutes.