How can I change the height of the NavigationView Header?

How can i reduce the space above and bellow the Header Text shown in my picture. I see that it comes from the DataTemplate for the header but I did not get it. Also https://learn.microsoft.com/en-us/uwp/api/windows.ui.xaml.controls.navigationview.header?view=winrt-22621 did not really help. I would also like to know how to align the Header Text left in one line with the blue content area bellow.

<NavigationView
    x:Name="NavigationViewControl"
    Canvas.ZIndex="0"
    IsBackButtonVisible="Visible"
    IsBackEnabled="{x:Bind ViewModel.IsBackEnabled, Mode=OneWay}"
    SelectedItem="{x:Bind ViewModel.Selected, Mode=OneWay}"
    IsSettingsVisible="True"
    ExpandedModeThresholdWidth="1280"
    DisplayModeChanged="NavigationViewControl_DisplayModeChanged"
    OpenPaneLength="160"
    IsPaneOpen="False"
    Header="{x:Bind ((ContentControl)ViewModel.Selected).Content, Mode=OneWay}">
    <NavigationView.MenuItems>
        <NavigationViewItem Content="Dashboard" helpers:NavigationHelper.NavigateTo="App.ViewModels.DashboardViewModel" Icon="Home" ></NavigationViewItem>
    </NavigationView.MenuItems>
    <NavigationView.HeaderTemplate>
        <DataTemplate>
            <Grid>
                <TextBlock
                    Text="{Binding}"
                    Style="{ThemeResource TitleTextBlockStyle}" />
            </Grid>
        </DataTemplate>
    </NavigationView.HeaderTemplate>
    <i:Interaction.Behaviors>
        <behaviors:NavigationViewHeaderBehavior
            DefaultHeader="{x:Bind ((ContentControl)ViewModel.Selected).Content, Mode=OneWay}">
            <behaviors:NavigationViewHeaderBehavior.DefaultHeaderTemplate>
                <DataTemplate>
                    <Grid>
                        <TextBlock
                            Text="{Binding}"
                            Style="{ThemeResource TitleTextBlockStyle}" />
                    </Grid>
                </DataTemplate>
            </behaviors:NavigationViewHeaderBehavior.DefaultHeaderTemplate>
        </behaviors:NavigationViewHeaderBehavior>
    </i:Interaction.Behaviors>
    <Frame x:Name="NavigationFrame" Grid.Row="2" Background="{ThemeResource SystemAccentColorLight2}" Padding="3" CornerRadius="8"/>
</NavigationView>

You need to override this resource:

<Thickness x:Key="NavigationViewHeaderMargin">56,44,0,0</Thickness>

You can override it as Page resource:

<Page>
    <Page.Resources>
        <Thickness x:Key="NavigationViewHeaderMargin">0,0,0,0</Thickness>
    </Page.Resources>
    <NavigationView />
</Page>

or inside your NavigationView:

<NavigationView>
    <NavigationView.Resources>
        <Thickness x:Key="NavigationViewHeaderMargin">0,0,0,0</Thickness>
    </NavigationView.Resources>
</NavigationView>

You can see how NavigationViewHeaderMargin is actually used in generic.xaml.