Overriding submenu placements

[jespersh]

I'm attempting to override the Placement set to Popup of submenus set here:

MaterialDesignInXamlToolkit/MaterialDesignThemes.Wpf/Themes/MaterialDesignTheme.Menu.xaml

Line 208 in 73fc217

Placement="Bottom"

It is quite easy to override the Menu's placement:

<Menu.ItemsPanel>
    <ItemsPanelTemplate>
        <VirtualizingStackPanel Orientation="Vertical" VerticalAlignment="Bottom" />
    </ItemsPanelTemplate>
</Menu.ItemsPanel>

I tried this without success:

<MenuItem.Resources>
    <Style TargetType="{x:Type Popup}">
        <Setter Property="Placement"
                Value="Right" />
    </Style>
</MenuItem.Resources>