Hgiles,
That's correct, in most airplanes when you lower more than 40º of flaps, the horizontal stab doesn't get enough airflow to be effective. It aggravates if you have a heavy nose airplane. In my airplane at least, I would not be able to raise the nose for flair in half rate mode unless I come much faster than necesary. Also we have to remember than not Spitfires models are the same or have being built the same way, so is hard to make a "general" rule.
Peter,
what do you mean by "porpoising on finals"?

JG