Telerik responded to my question with a solution that [somewhat] works. Here is what they wrote:
You may try to reset the Padding of TileListPanel - by default we set this value to 30 pixels on the top for the grouping functionality of this component. Directly setting this value to 0 will reset the distance on the top, as shown below:
<Setter Property="ItemsPanel">
<Setter.Value>
<ItemsPanelTemplate>
<telerik:TileListPanel Padding="0" AllowDrop="True" Background="Transparent" CanHorizontallyScroll="True" CanVerticallyScroll="False" IsItemsHost="True" telerik:ScrollingSettingsBehavior.IsEnabled="True" telerik:ScrollingSettingsBehavior.ScrollStepTime="0:0:0.05" ScrollOwner="{x:Null}" telerik:ScrollingSettingsBehavior.ScrollStep="24" telerik:ScrollingSettingsBehavior.ScrollAreaPadding="200"/>
</ItemsPanelTemplate>
</Setter.Value>
</Setter>
Also, I am pasting you the full template with this modification for RadTileList:
<Style x:Key="RadTileListStyle1" TargetType="{x:Type telerik:RadTileList}">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type telerik:RadTileList}">
<Grid HorizontalAlignment="Stretch" VerticalAlignment="Stretch">
<StackPanel Orientation="Horizontal">
<ContentControl x:Name="PART_PanoramaBackground" ClipToBounds="True" Content="{TemplateBinding PanoramaBackground}" HorizontalAlignment="Left" VerticalAlignment="Top"/>
</StackPanel>
<ScrollViewer x:Name="PART_ScrollViewer" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Background="{TemplateBinding Background}" CanContentScroll="True" HorizontalScrollBarVisibility="{TemplateBinding ScrollViewer.HorizontalScrollBarVisibility}" Margin="0" Padding="{TemplateBinding Padding}" VerticalScrollBarVisibility="Hidden">
<telerik:StyleManager.Theme>
<telerik:Office_BlackTheme/>
</telerik:StyleManager.Theme>
<ItemsPresenter/>
</ScrollViewer>
<ContentPresenter x:Name="dragVisualPlaceholder" HorizontalAlignment="Stretch" Visibility="Collapsed" VerticalAlignment="Stretch"/>
</Grid>
</ControlTemplate>
</Setter.Value>
</Setter>
<Setter Property="ItemsPanel">
<Setter.Value>
<ItemsPanelTemplate>
<telerik:TileListPanel Padding="0" AllowDrop="True" Background="Transparent" CanHorizontallyScroll="True" CanVerticallyScroll="False" IsItemsHost="True" telerik:ScrollingSettingsBehavior.IsEnabled="True" telerik:ScrollingSettingsBehavior.ScrollStepTime="0:0:0.05" ScrollOwner="{x:Null}" telerik:ScrollingSettingsBehavior.ScrollStep="24" telerik:ScrollingSettingsBehavior.ScrollAreaPadding="200"/>
</ItemsPanelTemplate>
</Setter.Value>
</Setter>
<Setter Property="GroupTemplate">
<Setter.Value>
<DataTemplate>
<Grid HorizontalAlignment="Stretch" VerticalAlignment="Stretch"/>
</DataTemplate>
</Setter.Value>
</Setter>
<Setter Property="SnapsToDevicePixels" Value="True"/>
</Style>
*Please give it a try and let us know how we can assist you further.
Regards,
Vanya Pavlova
Telerik*
Here are the results:
When I first launch the app:
If I resize it ever so slightly:
If I resize it a significant amount:
As shown in the image above, the tiles don't consistently stay positioned to the upper-left. For now, I will incorporate this code into my app, but I'm going to follow up again with Telerik and see if there is another layer in this solution.