I collectively put them as Nato . Russia cannot host any security bases in Nato countries . So pls check again .Russia has 14 immediate neighbours (https://en.m.wikipedia.org/wiki/Borders_of_Russia). All of them are at a distance of zero nanometres. So how can one of them (Greenland) be "closest" and another (Canada) come next? 14 are equidistant at a distance of zero.
Even if there is a "no man's land" like arrangement between some neighbours, they are still adjacent. The buffer zone is just a security/political arrangement.