entityRef widget seems to not respecting params
The entityRef widget uses the 'getlist' API action, so you can test it out by going to the API Explorer (in the Help or Support menu under Developer, or if you go to the CiviCRM path "civicrm/api/explorer").  


Select Contact as the Entity and getlist as the Action.  
Pick the Parameter API Params, and set the value to {'contact_type': 'Individual', 'id': {'IN': [132, 168, 169]}}.  


See what you get--in theory, that should just return those three contacts.  If so, your problem isn't the parameters; it must be the way your form is customized.

The code presented here looks good.  However, are you sure you removed the field you are replacing?  To replace a QuickForm element, you should remove the old one and generate a new one in its place.  To remove the old form, add this to the top of your code:

$form-&gt;removeElement('related_contact_id');


and then add the field.

An alternative method: since you're just replacing an existing entityRef field, it might be more efficient to just modify the API parameters.  The following Javascript might do the trick:

// Get rid of the old entityRef:
$('#related_contact_id').crmEntityRef('destroy');

// Generate a new entityRef:
$('#related_contact_id').crmEntityRef({
  api: {
    params: {
      contact_type: 'Individual',
      id: {IN: [132, 168, 169]}
    }
  }
});