Benson,
I have had some experience of writing tiny Italic (particularly on family trees) and as you have indicated, it can be very tricky. I don't know if it will help or not, but here are a couple of observations :-
The paper has to be smooth and uncoated. to avoid clogging up the nib.
The nib has to be constantly cleaned - far more often than with normal sized italic.
I haven't found that the choice of ink makes any great difference - perhaps I've just been lucky!
Most important of all is the nib to paper 45 degree slant. If this is out by the merest fraction, the turned nib will produce unacceptably thicken diagonal upstrokes.
Tiny writing with an edged nib can be difficult but immensely satisfying.
Ken