The bowline part of the pigtail is not to get in contact with the forestay with this setup. We spliced and stitched the pigtail into the core of the spi sheet, and that is the part of the spi sheet which passes the forestay. In practice, the bowline knot sometimes had to slide over the forestay, but we never had any trouble with that.
We started out with tying the spi directly to the spi sheet, and that also worked, but not as painless as with the pigtail setup. Just my experience.