My apologies, Southerlys... Apparently I have been providing inadequate space for the past 12 years to my birds.
No offense meant - LOL - chickens don't have much say in where they're kept. Please don't feel offended that I have an opinion as well. Again just an opinion of my experience. I believe there are just as many people in favor of this thinking as are opposed to it.
For what we feel are healthier reasons we give ours plenty of space. My folks raised chickens on the farm anywhere from 25-50 at a time in an open pen the size of a city block. Of course we had 25 acres then so that was easy to do and throw in some ducks and geese to boot. Chickens are messy but in a big area there is no offensive odor because of being on the move. Chicken addicts tend to overcrowd and that leads to pest infestations, illnesses, odors, unhealthy foot conditions - you name it. Because we kept our poultry on dirt and not shavings or litter or whatever, they were a healthy bunch and Mom did routine health checks. She always knew what animal was what and it still amazes me today how she knew them as she didn't tag them in any way. Today with our own girls we keep a soft dirt floor in the coop. If one should jump or get knocked to the floor it will be a gentler landing then a hard wood or concrete floor - again keeping our bantams in mind. Colder climates may not have this option but it works for us here. It's also wise to get the correct breeds for the climate zone.
Yes, Silkie bantams do really need the same space as LF. They are lower to the ground and if mixed with some LF need that same space to dodge the klutzier bigger LF because Silkies can't fly - only leap and jump. Our sweet kooky Ameraucana is notorious for being the biggest klutz in the flock and knocked a Silkie out of a nestbox ledge. Cost us $77.00 for vet visit and medicine for the poor little bruised bantam - we were just relieved nothing was broken and owe it to the fall on a softer dirt floor.
Everyone's situation is different and everyone chooses their own best methods. I just hate to see bantams classified as needing less space and bring awareness about coop space dwindles because of feed/water/nestbox/etc taking away the allottment. I loved the big U.K. Eglu when I first saw it and it wasn't the cost that was prohibitive but that the attached fencing easily collapsed when someone's German Shepherd jumped on it. Eglu was advertised for up to 10 LF and customers said it was barely comfortable for 2-3 hens and that the plastic ramp didn't even reach the ground so the chickens never used it. We were going to get a pre-fabricated coop but dimensions weren't enough for a rabbit IMO plus customer reviews said the assembly directions were just a page of unclear illustrations and that a lot of pieces would be damaged/split or parts were missing and didn't feel secure that the coops were predator proof in any way. For the same cost of a pre-fab we got a fully assembled custom-built coop at our feed store with the round-hole entrance nestboxes that gives hens the privacy they love. It was a chance random fluke finding it at the right place at the right time as we don't have the talents of many wonderful builders on this thread.
The insecurity of pre-fabricated housing is why I love seeing chicken owners making secure, ingenious, and spacious digs on this coop thread. Chickens aren't fussy about coop style but they do love space. I equate space for a chicken to being a human in a 10 x 20 space 24/7 eating, sleeping, not being able to choose my meals, and entertaining myself with only another two or more individuals and eventually going stir crazy. Chickens are mobile foraging creatures and as such need more space, not less. Thank goodness the old-style commercial caged egg hens are getting criticized and eliminated not just in the USA but all over the world - finally!