You can use InitialFolder property for this, for example:
//The path parameter should be in this format: [RootFolderName]:\some\path
fileManager.InitialFolder = "[RootFolderName]:\some\path";
Assume your structure is as follows:
Root
|--> Folder1
|--> Subfolder1
|--> Folder2
|--> Subfolder2
And if you set InitialFolder property to [Root]:\Folder2\Subfolder2, then FileUltimate shows the tree like this and opens that folder:
Root
|--> Folder2
|--> Subfolder2
So if RootFolderName and path is different for each page view then you can dynamically build the string accordingly and set InitialFolder to that string, for example:
var rootFolder = new FileManagerRootFolder();
rootFolder.Name = "Uploads";
rootFolder.Location = "~/uploads/";
//Build root string [Uploads]:\
var root = string.Format("[{0}]:\", rootFolder.Name);
//Get your folder or path from querystring
var path = Request.QueryString["folder"];
fileManager.InitialFolder = Path.Combine(root, path);