I don’t think the burial matters. It’s not random atoms that are turned into C14. It’s specifically nitrogen. And I think those interactions mainly happen in the mid atmosphere with cosmic rays. So it’s the atmosphere providing the shielding.
The Wikipedia page for this explains it pretty well, especially the Physical and Chemical Details section.



There’s like two people’s devices behind my router. The amount of benefit I get to hiding which device is sending traffic is pretty meaningless. And all my user devices are using privacy extensions anyway.
I don’t quite understand what you’re trying to prevent. Like if I have an iot device that doesn’t support privacy extensions, who am I making the tracking harder for by using ipv4? Anything the device talks to already is probably tracking via the device authenticating in the first place. And anybody in the middle doesn’t really learn much by knowing that a particular device is sending opaque traffic vs the house is sending opaque traffic.
Big tech tracks us because we voluntarily login to their services. And they do so mainly to sell us ads. If you don’t want them tracking you, hiding IP doesn’t help much. Like don’t login to their services and block requests to their domains to prevent third party site integrations. If you need to use their services anyway, then you’re fundamentally screwed.