your dimensions sound like the standard, but if you got the
wood and wire to space no rabbit ever refused the legroom to hop more than once. You asked how big vs what is the standardized minimum, i keep my giant chins in a really big pen that would infuriate most case breeders. I just find when they have litters it's a meat locker by harvest time, so i keep them in about 30 inches wide by 5 feet long by 4 feet high. I have open kennels so i can get in so it's not exactly a hutch, but i feel there's just
enough space for them to get enough back and forth that i don't feel like im keeping veal. I have 4 does and 1 buck, so there's always someone with a growling litter, I think if I had new zealands I would be happy with 3 feet by 3 feet there just not going to get to 12 pounds and stretch out to 2 feet long.
So i think your spacing's pretty normal and well tested, I know if I had caged rabbits i could fit 3 times the amount in the same space but I wouldn't be happy and id probably have rabbit problems i don't have now.