I've picked the following lines in bold from SAP help.
<b>"Note that the width of the main window must be the same on all pages. All other window types can have different sizes and positions on different pages."</b>
refer the corresponding link Page" target="_blank">http://help.sap.com/saphelp_47x200/helpdata/en/d1/802e84454211d189710000e8322d00/content.htm">Page Window
Can an Constant Window have different sizes and positions on different pages?