When interacting with the world objects in 3rd person this should function by placing your center of view on them, but fallout 4 also activates things that are 180 degrees from your center of view, so if your standing in front of a door for example, *facing your character and your view away from the door*, a prompt will appear to open the door. This is really annoying when you are trying to talk to campanions/loot in a confined space. You basically get double the loot/open prompts and you have to micromanage where your char is positioned in order to talk to someone correctly or pick up a certain object. Hope this makes sense to people and I hope it gets fixed, I think this was an issue in skyrim as well.

if you zoom out in 3rd person you can activate things 15 feet away

It's because 3rd person is a lie, it's 1st person with tweaks which change how your player is drawn and where the camera is in relation to him. You have the quirks you mention because it's still the invisible crosshairs and camera which does the targeting - the main reason 3rd person mode in Bethesda games feel bad, clumsy and floaty.