The RptViewerSize setting defines the screen size to display the Report Viewer in the .NET Report Manager.
By default, its size is based on the Keystroke Program window size (and is located the upper left corner of the Keystroke Program window). The format for the value is: W, H (width, height). The comma is mandatory. For example: RptViewerSize=1920,1080
sizes the viewer to 1920 pixels wide by 1080 pixels high. Note: if the
specified location is not on an active monitor then it is ignored.
Example: RptViewerSize=1920,1080