Hi,

If I understand the issue correctly, you're looking for a way to limit the results you're returning from a search to only include content from within a section of the site (in your example, either A or B depending on the site the user is currently viewing). I think the way I'd approach that would be to filter using Ancestors() to limit results to those with an ancestor of the required section. Something like this:

ContentReference ancestorContentRef;
if (currentSubsite == siteA)
{
    ancestorContentRef = contentRefOfSiteA;
}
else
{
    ancestorContentRef = contentRefOfSiteB;
}
var query = SearchClient.Instance.Search<MyContentType>()
    .Filter(x => x.Ancestors().Match(ancestorContentRef.ToString()));