I am working on creating an experiment around this right now through CSU. I am a 4-H Agent in Jefferson County and hatch chicks in local classrooms to teach youth about the life cycle.
I haven't had any problems hatching in the city but have had a terrible time hatching in the Mountains. I do get my eggs from local 4-H members who live in the city (I have never tried to order eggs from a lower elevation). The last test I hatched eggs in Conifer, with eggs that were laid in Conifer, all of them hatched but they all were splay legged so something went wrong. We tried to hatch eggs from Wheat Ridge at the Conifer school as well but not a single egg hatched. When cracked open all of the chicks were fully grown.
I use a R-Com 20 incubator to help control the temperature and humidity since schools often change temperature as they leave for the evening or weekend. The incubator is pretty expensive but if you are going to do much hatching it is certainly well worth the money!
I will be doing the experiments in April and May and will let you know what I find out. Hopefully this will help you have success in the future!