went to the LBS, advise for rack designers
All the racks I saw had 2-3" of space between the rack and the top of the front tire. To me they looked awkward and that is enough distance to make the performance suffer if there is any weight on the rack at all. It looked to me like they were mostly racks designed for the particular bike they were on, so it's not like they were using a generic rack. Even generic racks could fit more closely than that.
I agree, Unter. In contrast, if you look at a variety of constructeur or in-style bikes, some racks nearly sit on the fender.