<% control Fields %>
<% end_control %>
before, but that didn't work. Your point about FieldSet/Form classes made me try a couple more things, though.
This is what ended up working:
Which is bizzare, since it's the same thing? (or is it?)
I gave up on this not long after I posted this question, but your reply made me revisit this and I'm happy it did. Thank you! Have a good New Years : D