I still can not get the print centered in the virtual page.
I see from your screen shots that the crop button is up.
To get an equal split of the image into 4 segments, you need to have the crop button down so the image fills the printable area. This will, of course, affect the aspect ratio of the finished print and crop some of the image. That's the compromise that has to be made at present.
There is a rather tedious way to do what you want (I've done it in the past) by making 4 individual crops of the image. This can be done in the batch Filter and taking great care to get the pixel numbers exactly right in the crop.
If you want to follow this up, come back and I can explain in detail.
Otherwise we have to wait for MIke
I do have some changes/upgrades to the poster feature slated for the future that will make them much easier to use.
Terry