Position layer in the centre of document

I'm trying to copy a document from one open document to another which I have achieved, but how can I position it in the centre of the new document?

This is what I am using at the moment,

tellapplicationid "com.adobe.photoshop"

  settextNametonameofcurrent document

  setMainDocumenttocurrent document

  set {oldTID, AppleScript'stext item delimiters} to {AppleScript'stext item delimiters, "_"}

  setimageDoctofirsttext itemoftextName

  setSecondaryDoctodocument (imageDoc& ".PSD")

  logSecondaryDoc

  logMainDocument

  setcurrent documenttoSecondaryDoc

  duplicatelayer "Main Image" oflayer set "Dodge and Burn" ofSecondaryDoctobeforelayer "Main Image" ofMainDocument

  setcurrent documenttoMainDocument

endtell