Help with layout customization (Blank BS2) - nothing I'm doing is loading a new position or block

I want to have a position for a media player/slider and two modules beneath it WITHIN the Main Body Content BLOCK, above where the 'content' is loaded.

This is because I want the side-menu to be alongside the media player/slider - so putting it in a spotlight position above the Main Body Content Block doesn't achieve that.

Please see the attached image of what I want to achieve. The are outlined in RED is the main content block (and contains a side-bar position), the areas in YELLOW are new positions for media, and the area in GREEN is where the normal page/blog content should start to appear:





I have followed the customization video and tutorial in the BS2 documentation pages, but whether I try to load another spotlight block in to the Main Body Content Block or just simply try to add a custom position - nothing seems to work.

I have cloned the layout, copied the relevant content block file to local/tpls/blocks/ folder, and updated the templateDetails.xml

The only thing that works is that my HTML comment and a new DIV added to the duplicated content block file is appearing!



Here is my code to try to add just a custom position under the content area. This is just to test if the customization is working and not the layout I am after:

1 - In the cloned layout file (local/tpls/ds-default-content-right.php):

2 - In the content block file (local/tpls/blocks/ds-mainbody-content-right.php)
[code type="xml"]

....
// positions configuration
$mastcol = 'mast-col';
$sidebar1 = 'sidebar-1';
$sidebar2 = 'sidebar-2';
$custom = 'custom';
....