Steve doesn't really come on here any more so thought I'd help out. I have the intermediate size plate, I remember when I bought the IS there were three sizes that dealers seemed to fit, a standard plate, a large plate (that almost fills the gap) and a medium sized plate (which is the one I have). Not sure on it's exact size but I'll measure it for you and let you know. Here's a pic:
Oooops I've just notices he's Banned..... :duh:
Your plate looks just about right It'd be much appreciated having the size. :winky:
Cheers
Dave.