Are you sure it's 3 hull lengths and not 2? Edit
The ISAF RRS changed for the 2009-2012 publication. The 2005-2008 version specified the zone to be a 2 boat length radius circle and of course VSK reflects this 2 boat length zone. In VSK regattas the boats are "one-design" i.e. there are no mixed fleet races therefore, the 2 boat length radius is the same regardless of which boat is nearer the mark.
It is questionable whether or not a 3 boat length zone might be introduced in any future version of VSK because at is stands today the speed of VSK boats through the virtual water is nowhere near to scale with the distance between marks. (VSK boats move much faster between marks on a 1 mile leg than real boats under the same conditions.)
This subject of scale is discussed further at the article, How realistic is VSK racing?
When zones from two marks intersect Edit
Anyone can use the track editor to create a racing course. Normally the zone for two marks would not intersect but for some VSK race courses you sail there may be intersection of two zones. The auto-umpire does not distinguish one zone from the other for the purpose of determining rule violations. This can lead to inexplicable penalties.
If you sail a track with intersecting zones just don't take the penalties seriously. Such tracks are not representative of real life racing courses.