Regarding your first question, RadWindow's autosizing logic expects that the content in the template to be wrapped in a container with some size set - otherwise we cannot determine what the size of the content is. If, in such scenario, we put a pre-set size as you suggest, then the AutoSize feature will not work, which on the other hand would produce inconsistent behavior for the user. We will discuss this issue in our internal meetings, but at this point I cannot tell how or if we will cover this scenario.
As for your second question, such change would break the layout of the RadWindow titlebar - that is why we haven't implemented such functionality in the control. If you want you could try the solution given in this forum post, but please note that we do not support such modificiation:
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the Telerik team
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