CSV import into subclass of Member

<%- if @topic_view.topic.tags.present? %>
<%= t 'js.tagging.tags' %>: <%- @topic_view.topic.tags.each do |t| %> <%= t %> <%- end %>
<% end %>

SS 4.7.1

Question:

I have 3 subclasses of Member: Guide, Client and Agent and a model admin to manage each.

Currently when I import a CSV file of eg. guides data through the guides model admin, they all end up with ClassName Silverstripe\Security\Member instead of App\Web\Guide

I’ve tried adding in ClassName as a column, but it doesn’t help. Is there any way to get the imports to add the ClassName of the current model instead of the default?