Place the ends of each bundle on a board. Take a sharp knife and scrape several times the last 2" - 3" of the tails with the knife blade straight up at a 90 degree angle. This will remove about half of the fibers leaving less material to marry into the last of the twist. Use plenty of wax before starting the twisting process. I've been making 3 bundle flemish splice strings for 25 years and this method works. Sometimes I think I have removed too much but those strings seem to turn out the best.