Using og_vocab terms in views exposed filters

I have been trying to use og_vocab terms in some of my views exposed filters.
I am creating a view using EVA and loading in group content by contextual filters and relationships which works fine.
I am using og_vocab vocabularies and terms to create some subgroups.
e.g
Group 1, vocab x, terms subgroupa, subgroupb
Group 2, vocab y, terms subgroupc, subgroupd

What I wanted to do is when a user was looking at a view they'd see the group context and be able to filter by these taxonomy terms. Not rocket science you'd think but for the life of me I couldn't work out the configuration to get the filters to respect the group context.
I could set taxonomy = blank textbox in filters, or I'd check the box 'Render Views filters as select list', which would load in the terms in my exposed filters, but they wouldn't respect the group context.
I tried various contextual filters but couldn't work out how to expose only the appropriate terms.

As a workaround I have developed a hook_form_alter function as below.
My question is, am I missing some configuration which would allow me to do this within views, if not I wonder how this could be made more useful for the og_vocab project?

/*Implements hook_form_alter*/
function mymodule_form_alter(&$form, $form_state, $form_id) {

  if ($form['#id'] == 'views-exposed-form-[VIEW-NAME]-[WHICHEVER VIEW NUMBER]') {

    // Get the current og group context
    $current_context = og_context();
          
    //Get the vocabularies of the group(s), we need to do some looping if there was more than one vocab per group
    $current_vocab = og_vocab_relation_get_by_group('node', $current_context['gid']);
    $current_vocab_vid = $current_vocab[0]->vid;
          
    //Query the taxonomy_term_data table
    $terms= db_select('taxonomy_term_data') 
    ->fields('taxonomy_term_data', array('name', 'tid'))
    ->condition('vid', $current_vocab_vid)
    ->execute()->fetchAll(); 
          
    //Build an array for the dropdown list
    $dropdown_array = array("All" => t("- Any -")); 
    foreach ($terms as $item) {
      $key = $item->tid;
      $value = $item->name;
      $dropdown_array[$key] = $value;
    }
     
    unset($form['og_vocabulary_target_id']);
    $form['og_vocabulary_target_id'] = array(
      '#type' => 'select',
      '#default_value' => 'All',
      '#options' => $dropdown_array,   
       );
  }
}