Is fixed: true working for editable elements?

It worked for us in v2, but in a project now in v3, we can't get fixed:true to work on editable elements such as editable_text or editable_file.

The setup

In our index.liquid file, we have something like this:

{% block 'site_settings' %}
  {% block 'map' %}
    {% capture map_text %}{% editable_text 'map', format: raw, fixed: true %}..{% endeditable_text %}{% endcapture %}
  {% endblock %}

  {% block 'slider' %}
    {% capture slider_text %}{% editable_text 'slider_text', format: raw, rows: 3, fixed: true %}...{% endeditable_text %}{% endcapture %}
    {% capture slider_image_1 %}{% editable_file 'slider_bild_1', fixed: true %}slider/home-4.png{% endeditable_file %}{% endcapture %}
  {% endblock %}
{% endblock %}

We're not using site_metafields because we haven't gotten them to work yet.

Even though we're using fixed: true, those editable elements appear on the editor for all pages that inherit from the index. Any ideas on how to get the correct behavior working?