How can I follow relations in ElementCriteriaModels from plugin code?
You're very close! Try this:

$criteria = craft()-&gt;elements-&gt;getCriteria(ElementType::Entry);
$criteria-&gt;section = 'concepts';
$criteria-&gt;limit   = null;
$criteria-&gt;relatedTo = array(
    'targetElement' =&gt; $e,
    'field'         =&gt; $field
);
$elements = craft()-&gt;elements-&gt;findElements($criteria);


Keep in mind, in this instance, $field is the field object which can be retrieved with something like the following:

$singleFieldModel = craft()-&gt;fields-&gt;getFieldById($singleField);


See the documentation (https://craftcms.com/classreference/services/FieldsService) for other ways to get a field object.