You shouldn't be able to invade someone if they are within very close proximity of any of the boss doors/fog walls, it's pretty annoying to wait 10 minutes only to invade a host that's abusing the fog walls, usually with 1 or 2 other summons as well.

It's also annoying to constantly be invading worlds where you are immediately kicked out because the host entered the boss room, which wouldn't happen if a small zone was set near each fog wall that temporarily prevented invasions.

Removing the possibility of invading a host obviously abusing a fog wall or about to enter the boss room would make many more invasions a lot more fun for both sides and save a ton of time (time queueing as well).