> So this is the NZ longest line right

Yup. I'd think so.

> It doesn't always make a difference, but it sometimes can.

I guess the obvious case is if there's a point near one end that is higher, but less than 1.65m higher.

It really might be better to use ground level at both ends. Or at least the same height at both ends e.g. if there is a person on both peaks.