Change height of GridSplitter preview - wpf

Question

I have a WPF GridSplitter with a controltemplate being applied to add grips and buttons. The height is set to 20px. When I drag the splitter to resize my grid the preview is also 20px. I'd like to change the height of the preview while it's being dragged.
Is there a simple way to accomplish this?
<Style TargetType="{x:Type GridSplitter}" x:Key="AdvancedGridSplitter">
<Setter Property="Background" Value="{DynamicResource {x:Static themes:PropertyGridCommonDictionary.SummarySplitterBackgroundBrushKey}}" />
<Setter Property="BorderBrush" Value="{DynamicResource {x:Static themes:DockingCommonDictionary.DocumentTabBorderNormalBrushKey}}" />
<Setter Property="BorderThickness" Value="0,1" />
<Setter Property="Height" Value="20" />
<Setter Property="HorizontalAlignment" Value="Stretch" />
<Setter Property="ResizeBehavior" Value="PreviousAndNext" />
<Setter Property="VerticalAlignment" Value="Center" />
<Setter Property="UIElement.SnapsToDevicePixels" Value="True" />
<Setter Property="UIElement.Focusable" Value="False" />
<Setter Property="ShowsPreview" Value="True" />
<Setter Property="Control.Template">
<Setter.Value>
<ControlTemplate>
<Border x:Name="Root" BorderThickness="{TemplateBinding Border.BorderThickness}" BorderBrush="{TemplateBinding Border.BorderBrush}" Background="{TemplateBinding Panel.Background}">
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="Auto" />
<ColumnDefinition Width="*" />
<ColumnDefinition Width="Auto" />
<ColumnDefinition Width="*" />
<ColumnDefinition Width="Auto" />
</Grid.ColumnDefinitions>
<StackPanel Grid.Column="0" HorizontalAlignment="Center" Margin="2,0,0,0" Orientation="Horizontal" VerticalAlignment="Center">
<ribbon:Button Context="StatusBarItem" Cursor="Arrow" ImageSourceSmall="/Resources/Splitter/SplitterSwitch.png" ImageSourceSmallSize="11,11" Padding="2,0" />
</StackPanel>
<Grid Grid.Column="1" />
<StackPanel Grid.Column="2" HorizontalAlignment="Center" Orientation="Vertical" VerticalAlignment="Center" x:Name="Grip">
<Rectangle Fill="{DynamicResource {x:Static themes:PropertyGridCommonDictionary.BorderBrushKey}}" Height="1" Margin="1" Width="50">
<Rectangle.Effect>
<DropShadowEffect BlurRadius="1" Color="White" Direction="90" Opacity=".8" ShadowDepth="1" />
</Rectangle.Effect>
</Rectangle>
<Rectangle Fill="{DynamicResource {x:Static themes:PropertyGridCommonDictionary.BorderBrushKey}}" Height="1" Margin="1" Width="50">
<Rectangle.Effect>
<DropShadowEffect BlurRadius="1" Color="White" Direction="90" Opacity=".8" ShadowDepth="1" />
</Rectangle.Effect>
</Rectangle>
</StackPanel>
<Grid Grid.Column="3" />
<StackPanel Grid.Column="4" HorizontalAlignment="Center" Margin="0,0,2,0" Orientation="Horizontal" VerticalAlignment="Center">
<ribbon:Button Context="StatusBarItem" Cursor="Arrow" ImageSourceSmall="/Resources/Splitter/SplitterVertical.png" ImageSourceSmallSize="11,11" Padding="2,0" />
<ribbon:Button Context="StatusBarItem" Cursor="Arrow" ImageSourceSmall="/Resources/Splitter/SplitterHorizontal.png" ImageSourceSmallSize="11,11" IsChecked="True" Padding="2,0" />
<ribbon:Button Context="StatusBarItem" Cursor="Arrow" ImageSourceSmall="/Resources/Splitter/SplitterMinimize.png" ImageSourceSmallSize="11,11" Padding="2,0" />
</StackPanel>
</Grid>
</Border>
<ControlTemplate.Triggers>
<Trigger Property="VerticalAlignment" Value="Stretch">
<Setter TargetName="Grip" Property="Orientation" Value="Vertical"/>
<Setter TargetName="Grip" Property="Visibility" Value="Visible"/>
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>

Answer 1

You need to set the PreviewStyle on your GridSplitter:
PreviewStyle="{StaticResource AdvancedGridSplitterPreview}"
An appropriate style could be:
<Style TargetType="{x:Type Control}" x:Key="AdvancedGridSplitterPreview">
<Setter Property="Height" Value="4"/>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate>
<Grid>
<Rectangle>
<Rectangle.Fill>
<SolidColorBrush Opacity="0.4" Color="Black"/>
</Rectangle.Fill>
</Rectangle>
</Grid>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
See here in the MSDN for another description with example.
Hope this helps.