I was wrong on the Leftovers. I tested Figy Berry, Sitrus Berry and Leftovers in the battle tower. All of them scale off the base health, so Figy Berry is 16,5%, Sitrus Berry is 12,5% and Leftovers is 3,125% in (level 10) dynamax form. Does someone know how Leech Seed on a dynamaxed pokemon works?