The first shows Masked Island a very small island which is part of the Auckland islands (one of the sub antarctic islands ). The snapshot shows the geonames tag and a snapshot of my fsx sim just hovering over the actual island location and as you can see the current xpoi marker is way across the bay.
I checked the coordinates in your screenshot and, according to Google maps, you should be over the actual island but, in the middle of the water between the big island and the small one, facing East so you should see the XPOI marker in front of you, which is exactly what you are seeing.
https://goo.gl/maps/YLDR7323wFxpEaQX7So, the thing that is not precise, seems to be the FSX scenery underneath.
The second set of images are of the Massey University School Of Aviation building located in Palmerston North Airport , New Zealand. First the geonames tag and then the fsx location with no XPOI label...
This is a bit strange, XPOI surely works only online so, if something it's on geonames.org, it should display on XPOI as well. What's your setting for "POI with inexact coordinates" ?