If you bend over from the waist and have a very rounded back to touch your toes it's mostly a back stretch (forward bend) and not a hamstring stretch. I don't know about your goals, but for me hamstring flexiblity it a lot more important (actually I barely work on back flexibility). So for me it's a lot more important how far I can get down with my back straight than being able to touch the toes with a rounded back (By now I can actually touch my toes with my back straight without being warmed up but I had to work a lot for that!)

So keep the difference in mind when working on touching those toes 🙂