I am sorry, I do not find anything in the wiki regarding Tagging for the renderer or Tagging for the router that is related to where we put nodes on a building. The rule is to put things as close as possible to where they are, so you should put the POI node as near as possible to its entrance. Putting the node in the centroid of the building is the default when you don't know where the entrance is, but when you do know, you should put it next to the entrance (more precise, more accurate)