In a 4' x 4' coop, for nine hens I'd use two roosts that reached all the way across. Put one about 12” from one wall and the other 12” horizontal away from that. That should give your breeds plenty of room to roost.
The general recommendations are between 8” to 12” per chicken. They don’t need that much room once they are settled in for the night, but they need extra room to get up there and move around to get to their favorite roosting spots. You have enough chickens that 9” to 10” each should be enough but that’s more than 4’ so that’s why I suggest two roosts all the way across.
The higher the roosts, the more clear landing space they need when they spread their wings and hop down so try to keep them as low as reasonable. They need to be higher than anything you don’t want them sleeping in, like nests. They poop a lot while asleep. The way I determine roost height is to determine the height of the floor, including any bedding, then position the nests. Then make the roosts a little higher than that.
In that tight space you might consider putting your nests under the roosts and use the top of the nests as a droppings board. They do pop a lot at night. If you can collect that poop it is great in compost and can significantly delay how often you need to clean the coop.
I addressed some of this in that link in my signature, but the more you crown them, the harder you have to work, for example in poop management. The more you crowd them the more likely you are to have behavioral problems that can range from bullying or feather-picking all the way to cannibalism. The less space you have the less flexibility you have in dealing with any problems that pop up.
