Binding ElementName inside a DataTemplate

I am trying to bind a property that is dependent on a control within the same DataTemplate.

To illustrate:

<DataTemplate>
    <StackPanel Orientation="Horizontal">
        <ComboBox x:Name="ComboList"
                  ItemsSource="{Binding StatTypes}"
                  SelectedItem="{Binding SelectedStatType, Mode=TwoWay, FallbackValue='Select a type'}">
            <ComboBox.ItemTemplate>
                <DataTemplate>
                    <TextBlock Text="{Binding Text}"/>
                </DataTemplate>
            </ComboBox.ItemTemplate>
        </ComboBox>

        <TextBox Grid.Column="1" MinWidth="40" Margin="5">
            <TextBox.Text>
                <Binding Path="StatValue">
                    <Binding.Converter>
                        <converter:PercentageConverter SelectedStatType="{Binding ElementName=ComboList, Path=SelectedItem}" />
                    </Binding.Converter>
                </Binding>
            </TextBox.Text>
        </TextBox>
    </StackPanel>
</DataTemplate>

But the property in the PercentageConverter is never set through this and I don't see why. Is this a naming scope issue? If so, I thought this would not matter since it is in the same DataTemplate If not, what am I doing wrong?