Example of how to change the size of the AdMediatorControl depending on the device width.

AdMediatorSizeByDevice.xaml

<Grid>
    <Universal:AdMediatorControl x:Name="AdControl"
                                 Id="ecba2d7a-f2d9-43bb-ab12-f8c5df300987"
                                 Height="90"
                                 Width="728" />

    <VisualStateManager.VisualStateGroups>
        <VisualStateGroup x:Name="VisualStateGroup">
            <VisualState x:Name="Mobile">
                <VisualState.StateTriggers>
                    <AdaptiveTrigger MinWindowWidth="320" />
                </VisualState.StateTriggers>
                <VisualState.Setters>
                    <Setter Target="AdControl.Height" Value="80" />
                    <Setter Target="AdControl.Width" Value="480" />
                 </VisualState.Setters>
            </VisualState>
            <VisualState x:Name="Desktop">
                <VisualState.StateTriggers>
                    <AdaptiveTrigger MinWindowWidth="720" />
                </VisualState.StateTriggers>
                <VisualState.Setters>
                    <Setter Target="AdControl.Height" Value="90" />
                    <Setter Target="AdControl.Width" Value="728" />
                </VisualState.Setters>
            </VisualState>
        </VisualStateGroup>
    </VisualStateManager.VisualStateGroups>
</Grid>