I apologize for the delay in this reply. My personal life has just been really busy lately. Hopefully I'll be able to answer your question. There really is a tradeoff between time and accuracy when it comes to the size of your graffiti characters. Unless your hands are a great deal quicker than mine, it would be very difficult to achieve this time writing full sized characters. I've found that I write best when I use apprx. 40% of the writing area for my characters. The trick is just to have very well defined strokes and not have any extra movements when you write your characters.
Jean was kind enough to send me a fitaly stamp the other day so I look forward to posting those scores before the contest is over!