Krisu13, You might want to reread Jake's advise. Wouter is giving you the optimum number for where to place the bail based on a sail cut specifically for your configuration. All the F18/20/16 etc have specified pole lengths spin size etc.. so yes if your spin is designed to go there it will work fine. But if you are using a spin from a different class and/or a different pole then this might not be the best place for using the sail.
If you want to have the best luck keeping the top of your mast intact though leave it where Wouter specified then recut the sail after you have the boat set up.
This is the reason this height is used. It is the best compromise for not breaking a mast.

What Jake offered was where to put the bail based on the shape of the sail for best sail shape.

Personally I'd place the bale on Wouters advise and then place the blocks where you want them (shroud, rear beam etc..) and have a sail maker look at the chute on the boat and cut the corners to fit the boat right.

I have gone through rigging a spin on a Hobie 18 and this is how I ended up doing it after much trial and more errors.