There is unfortunately no hard and fast rule
Are you going to use a 2:1 halyard
and/or a torque rope
. Those both make the system work
better and increase tolerance to measurement imperfections.
But you are better off getting the hoist just as high as you can. It’s a light air sail and that gets you more area up high where you want it, and it makes furling
better. Are you buying
new - in which case the mfg or dealer should be able to give you a length within cm’s, and if buying used can’t you ask the broker or seller to let a sailmaker
to measure it? Has your sail loft network never fit a code sail to this model (which is not an obscure uncommon boat) before - they should have a measurement in their design files.
Bottom line, you can probably easily get away with a meter of halyard
showing, but it’s not “right” and you will sail better and and the furling will work
better with tighter measurement.