Modifying the source for my metadata navigation

Question

I have an Enterprise Wiki site collection that contains 5 sub sites. and i want to enable filtering the main site collection and the 5 subsites using metadata terms. to do so , i did the following:-
1. i have enabled the meta data navigation for the 5 sub sites and the main site.
2. i have enabled tree view for the 5 sub sites and the main site.
3. finally i have added the following web part , which will do the redirect , when clicking on any term inside the metadata tree:-
public VisualWebPart1()
protected override void OnInit(EventArgs e)
var request = HttpContext.Current.Request;
var response = HttpContext.Current.Response;
if (!String.IsNullOrEmpty(request.QueryString["TreeField"])
&& !String.IsNullOrEmpty(request.QueryString["TreeValue"]))
response.Redirect(String.Format("{0}?TreeField={1}&TreeValue={2}",
SPContext.Current.ListItem.ParentList.DefaultViewUrl,
request.QueryString["TreeField"],
request.QueryString["TreeValue"]));
else if (!String.IsNullOrEmpty(request.QueryString["TreeField"]))
response.Redirect(String.Format("{0}?TreeField={1}",
SPContext.Current.ListItem.ParentList.DefaultViewUrl,
request.QueryString["TreeField"]));
base.OnInit(e);
protected void Page_Load(object sender, EventArgs e)
the problem i am facing is regarding the source for the filtering, for example if the user is inside the main site and he clicks on one of the terms , then only the pages that are within the current site collection and have the selected term, will be displayed,
while i want to include all the sub sites in the filtering  . so can anyone advice on this please?
in other way , i am trying to have the same behavior in the defualt search. as currently if i am inside the root site for the site collection and i search for certain word,  SharePoint will search the main site and all the sub sites for the word, while
if i am inside certain sub site only pages within that sub site will be searched. while in the metadata navigation and filtering if i am inside the main site and i want to filer based on certain term, then only pages within the main site will be filtered ,
rather than including all the sub sites pages...

Answer 1

Can anyone advice on my question, as i can not find any documentation that talks about changing the content source of the metadata navigation. so that i can specify to include all the sub sites , when filtering pages using the metadata navigation ??? please
any advice ?