You're right there's no measurement given for the position where the rope comes out of the pole. It will vary depending on the type and position of the chute mouth, so you need to work it out for your setup.

Having said that, if you have the usual triangular chute mouth fitted on the bridle then right under the chute mouth is usually the spot for it.

Things to consider are:

It's best not to have it forward of the bridle as the back-to-back pulleys can possibly go through the loop supporting the pole when the spinnaker comes down, which could cause a snag when you try to pull it up again.

I have mine set up so that the back to back pulleys run all the way out to the hole in the side of the pole. There's no more tack line left then and they can go no further. At this point the spinnaker tack is tied so that it just goes into the chute mouth. This stops the spinnaker going any further into the chute, and prevents it going out of the back of the sock under the trampoline.