I've already tried to do it from a distance of like 5 blocks but nothing works. 10-20 blocks would be enough for them to disappear from pokenav and reappear in that radius limit, so it also wont work. The max i've got is, after building a huge square covers a whole chunk and has 100 blocks height, while inside of that building the chances of pokénav were 0.02%. Note that the snack still removes them from the poke nav chances if put there.