presentModalViewController in UISplitViewControllers detailView not presenting the view in full screen

I have added the UISplitViewController view in my mainViewControllers view, the code is below.

    documentsRootViewController = [[DocumentsRootViewController alloc] initWithStyle:UITableViewStylePlain];
    UINavigationController *navigationController = [[UINavigationController alloc] initWithRootViewController:documentsRootViewController];
    documentsRootViewController.title = @"Document List";

    documentDetailView = [[DocumentsDetailView alloc] initWithNibName:@"DocumentsDetailView" bundle:nil];
    documentsRootViewController.detailViewController = documentDetailView;

    docSplitViewController = [[UISplitViewController alloc] init];
    docSplitViewController.viewControllers = [NSArray arrayWithObjects:navigationController, documentDetailView, nil];
    docSplitViewController.delegate = documentDetailView;

    CGRect splitViewFrame = CGRectMake(0, 0, cetralArea.frame.size.width, cetralArea.frame.size.height);         
    docSplitViewController.view.frame = splitViewFrame;
    [cetralArea addSubview:docSplitViewController.view];

now what I want is to present a ViewController from the DetailView of the UISplitViewController I am trying to do it as below inside the DetailViewControllers Click Me! buttons click.

- (IBAction) buttonClicked:(id)sender
{
    NSString *phrase = nil; // Document password (for unlocking most encrypted PDF files)    
    NSArray *pdfs = [[NSBundle mainBundle] pathsForResourcesOfType:@"pdf" inDirectory:nil];    
    NSString *filePath = [pdfs lastObject]; assert(filePath != nil); // Path to last PDF file

    ReaderDocument *readerDocument = [ReaderDocument withDocumentFilePath:filePath password:phrase];    
    if (readerDocument != nil) // Must have a valid ReaderDocument object in order to proceed with things
    {
        ReaderViewController *rViewController = [[ReaderViewController alloc]