Since it is known that the "X" in the top right to close the box causes the problem, I have used another approach and it solves the preview window size also.

At the beginning of the main program I create a form and remove some of the controls and force a maximized setting so the report never show up as half a screen.

public Rep_Preview
Rep_Preview = createobject( "form" )
With Rep_Preview
   .Caption = "Report Preview"   && or whatever you want 
   .Closable = .F.
   .Controlbox = .F.
   .MaxButton = .F.
   .MinButton = .F.
   .Name = "MyPreviewWindow"   && used in the report command
   .WindowState = 2   && always in maximized mode
   .Visible = .F.
EndWith

Then when actually running the report command, just add the window name

report form preview window "MyPreviewWindow"

This way the user can never click on the top right "X" to close the window and the window will always be in the maximized state.