When AutoSize is enabled on a RadWindow, the calculated width and height of the window can be larger than the actual content requires. The extra size appears as dead space around the content, on the right side for width and at the bottom for height, and is most noticeable when the content or its wrapping container has its own padding or border.

Steps to reproduce:

• Add a RadWindow with AutoSize="true" (any AutoSizeBehaviors).
  
• Set the window content either through a ContentTemplate with inline markup (for example a RadAjaxPanel), or through NavigateUrl pointing to a separate page.
  
• Give the content, or its wrapping container, a horizontal and/or vertical padding or border via CSS.
  
• Open the RadWindow and let it auto-size.
  

Result:
The RadWindow is wider and/or taller than necessary. The extra space is not evenly distributed and shows up as unexpected empty space next to or below the content.

Expected:
The RadWindow width and height should match the actual content size, with the same behavior as before the 2026 Q1 release.