3 boats length

The rule is normal position, so if you routinely set the pole before the mark it may count. But it may be less of an issue now, because there are fewer boats where the pole both extends significantly beyond the bow and is set separately from the kite. I also have a feeling that whereas two boat lengths felt about right to get the pole out early for a fast hoist, three boat lengths kinda feels a bit soon.

Originally posted by sargesail I think the sprit withdrawal and boat getting shorter is probably why the rule refers to hull lengths and hull entering the zone.

I'm sure you're correct. The trick in the detail is that bowsprits, spinnaker poles etc can (if the position can be said to be normal) make overlaps even though they don't affect the radius.

There's a new Q&A to clarify

I've always understood it to be 3 of the leading boat's lengths, as the FF would arrive at 3 boat lengths well before the oppie is anywhere near the zone. However, I've heard people argue it the other way, including a coach assessor.
As for the other, if, and it would have to be terribly light winds, the 400 pulled the sprit in and actually left the zone he formed with the sprit out, he would be in the same position as anyone leaving the zone. However, if he just gets shorter in the zone he created, then there is no problem.