yeah i know, i put koni fsd and eibach pro kit a couple of months ago but it didn't lower it enough.
What is a good spring to use with fsd's that would lower a bit more.
have a search for negs car, he runs H&R springs with his FSD's and the ride height is spot-on 
....Yes, it's important not to use springs which lower beyond the FSD's capabilities - Otherwise you could have a nasty mishap!
Your best bet is to contact Koni and find out properly.
Someone I know of had such a problem and it didn't manifest itself immediately.