Layout builder: nest one column within another

I need to be able to nest columns within each other and am having problems. I have a 1/4 + 3/4 layout, and would like to be able to put to 50% columns into the 3/4. They need to be editable with the drag-and-drop editor — it’s not ideal for me to just paste the shortcode into a text widget.

I was editing \config-templatebuilder\avia-shortcodes\columns.php and added the code below that you see at the bottom of this post. This allowed me to nest my new 1/2 column within the 3/4 just as I’d expect. However, when I save the page, it removes my nested column and places it adjacent to the 3/4 rather than inside it. I assume this is some setting in \config-templatebuilder\avia-template-builder\assets\js\avia-builder.js that I need to change, but am not sure what it is. I know this falls out of official theme support, but I’m really stuck and would appreciate guidance on what I need to change.

if ( !class_exists( ‘avia_sc_columns_one_half_inner’ ) )
{
class avia_sc_columns_one_half_inner extends avia_sc_columns{

function shortcode_insert_button()
{
$this->config[‘name’] = ‘1/2 inner’;
$this->config[‘icon’] = AviaBuilder::$path[‘imagesURL’].”sc-half.png”;
$this->config[‘tab’] = __(‘Layout Elements’, ‘avia_framework’ );
$this->config[‘order’] = 90;
$this->config[‘shortcode’] = ‘av_one_half’;
$this->config[‘html_renderer’] = false;
$this->config[‘tinyMCE’] = array(‘name’ => ‘1/2 + 1/2’, ‘instantInsert’ => “[av_one_half first]Add Content here[/av_one_half]\n\n\n[av_one_half]Add Content here[/av_one_half]“);
$this->config[‘tooltip’] = __(‘Creates a single column with 50% width’, ‘avia_framework’ );
$this->config[‘drag-level’] = 3;
$this->config[‘drop-level’] = 2;
}
}
}

Thanks very much!