Hi Steve,
My understanding of the new rules is that the new ‘zone’ (previously known as a two length zone) is now defined as ‘the race around a mark within a distance of three hull lengths of the boat nearer to it…’ so the standard, unless stated differently in the SIs is now 3 hull lengths.
The organisers can choose to extend to 4 lengths or reduce to 2 lengths, but my view would be that, unless we can think of a good reason to change, we should stick with the standard
Cath