Alternatively don't bother making a split tail in the first place

Just attach the end of the line to one side and use a bit of thin dyneema to make a loop around the line to the other attachment point. Adjust the length of the loop to make the perfect pigtail without the aggravation of splitting it.

(my mainsheet is coreless, making it difficult to make a pigtail without making the line fatter by inserting a core)