Very nice.
You might perhaps find the following thread interesting reading. Although the thread is a request in the FontCreator - Requests and Enhancements section of the forum, that request is to automate something that can be done manually now, namely enlarging the scanned image before importing it into FontCreator. That enlarging seems to give the FontCreator software something more to process and results can sometimes improve, even though the same underlying image information is being used.
On a different aspect, you might like to know of the work of the Medieval Unicode Font Initiative. I do not know if that is relevant to what you are trying to do, yet as it might be the same historical period I thought that I would mention it so that you can have a look if you choose to do so.
I hope that this helps.
William Overington
6 December 2010