The AutoSize functionality is designed so that it keeps the entire RadWindow visible. If the content is larger than the available space the RadWindow itself will have scrollbars. This behavior is intentional so that parts of the popup are not hidden automatically, which would be percieved as buggy behavior by the end user.
What you can do is to use the RadWIndow's client-side API
//the first parameter is the horizontal position, you can keep it centered like this:
//centers the RadWindow so that this calculates the x-position for you
//you can change the 0 to some offset from the top of the browser
How to determine if you need to executet his logic (i.e. what is the size threshold) depends on your custom logic and needs.
the Telerik team
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