Let me see if I can make you feel better about one thing. My nests are 2 feet and 4 feet above the coop floor, broodies hatch in them all of the time. I once saw a hen get her chicks down from a 10 feet high hay loft. The hen flies to the ground, tells the chicks to jump, and they do. Whether from 2, 4 or 10 feet up, they hit the ground, bounce up, and run to her. They do not get hurt.
I've only had chicks fall out of a nest one time. I was using a 7-1/2" x 11-1/2" cat litter bucket as a nest. It was about 4 feet above the coop floor. The chicks were crawling up on the hen's back. She was sitting so close to the side of that nest that when a chick fell off of her back it missed the nest and hit the floor. Four different times I picked a chick up off of the floor and put it back in the nest. It was probably the same chick each time. It was not injured in those falls. Don't worry about the chicks being hurt if they fall off of or roll down that ramp. They will be OK when the hen takes them down.
The chicks may not be able to get back up to the coop once she takes them down. Be out there at their bedtime to see if the hen needs help getting her chicks where she wants them and where you want them. My coop is on the ground so no ramp but I'm out there at bedtime every night to lock them up anyway but occasionally my broody hens need a little help. Yours might or might not.
When those chicks were falling out of the nest I had a rooster, several hens, and a lot of juveniles running around. When a chick is separated from the hen it is in some danger from the other flock members but I never had a problem. The chick did not go that far that the mother could not protect it anyway but the others were not that interested in it anyway.