I'd like the page being loaded into the radwindow to have the responsibility of setting the size of the radwindow before the radwindow is displayed so the user doesn't see it getting resized. Is this possible?
I am not quite sure about your requirement. But, have you tried setting the Height and Width properties of radwindow to required?
Also you can set the width and height using the client side methods set_width and set_height. Checkout the following documentation for more information about the client side methods and properties.