Turkey - the dimensions of those cages are an exact copy of mine (that is where the similarities end) and "what size is best" is probably the most common question I get. The reason they are narrow is because many years ago in a western desert two guys experimented and found it was fairly easy to get them into cage traps that were more narrow then the standard 18X18 trap available. Ten inches wide is what they settled on and then, in order to get more into a truck bed they made one a little smaller and one a little bigger. Most guys think bigger is better as it will make the cat more comfortable entering it. Perhaps true for some animals but not for cats. Size doesn't much matter.
Most guys running my stuff and making yearly good catches of cats out here like the smaller ones best because they hide better and fit into tight places. In fact getting big toms into the narrowest cage is actually the second easiest cat to catch. The easiest is the second cat into the same cage because of all the enticing cat smells inside. Most folks calling me for their first "cat cage" always want the biggest one for the reason previously mentioned, confidence. It really doesn't matter much as it is up to you to lure the cat in. The smallest one is a little more selective as it catches fewer dogs, pigs etc. The biggest one can be used to catch more dogs, , ,

Any of the sizes are fine. Ten inch is a happy spot.

ML