Wouter-
F 18HT's I would expect to be better for "smaller" sailors due to the lighter boat and sheet loads. Easier to right (I assume) and move around on shore, shorter, lighter daggerboards. Ability to have flatter sails than a heavier crew.
Same reasons a F 16HT is easier on smaller persons than a Hobie 16 (IMO). I think this is a great thing for all the new "lightweight" boats-