Some people suggest 7" per adult bird, some think 15" is the minimum required. I've even seen 24" as a suggestion. In my opinion, each flock is unique and has their own dynamics. I'm not a huge fan of magic numbers as they work like magic for some but not for others. Still, if you look at them as guidelines it gives you a starting place. You may find you need to be a bit flexible as it all plays out no matter where you start.
Chickens tend to want to roost at the highest spot available. That means there will probably be some competition for the top spots. The ones highest in the pecking order get to sleep where they want and can sometimes be pretty brutal when enforcing those pecking order rights. That is actually pretty normal, even with adults. When I have 8 adults on 16' of roost space I see that. As yours go through adolescence and the pecking order changes it could get exciting. I just let mine work it out. As far as mine are not sleeping in the nests and are sleeping somewhere safe from predators I don't care where mine sleep.
A possible issue is how high are your nests. If your lower roosts are higher than the nests you will probably be OK. If your nests are too high they may decide to sleep in the nests instead of on your lowest roosts. Sometimes those pecking order disputes get rough enough that some leave the roosts and look for a safer spot. Time will tell.
I don't know how old yours are. I'd expect as many as can will crowd onto the top roost, with the others arranged below. As they get bigger and the room on top gets tighter, some will be forced down. They may all stay on that ladder roost, or some may look somewhere else as they get forced further down. The layout of your coop could have an effect on that. Or just flock dynamics. With 19 hens and 5' roosts I'd expect all of them to wind up on your top three roosts. Of course, I've been wrong before.
The general recommendation for roosts is that they are horizontally separated from the wall or each other by 12". That's a center-line dimension, not edge to edge. I think your dimensions are elevation, not horizontal, so not sure how close to the "ideal" you are. That 12" gives them plenty of room to position themselves. They can sleep in less. The typical recommendation for vertical separation on a ladder style roost is 12". I'm not sure why. Chickens can easily hop up and out 12" without even flapping their wings though most will spread them. Maybe that has something to do with it. Sometimes a bully will peck down at another chicken, maybe 12" makes it a little harder to do that. Maybe someone just suggested the number, 12" is a standard building dimension, it works, so it became a guideline. I would not worry about your 10" yet, just see what happens.
Bottom line, I think you will be OK as you are, but with living animals you don't get guarantees.. I would not do anything dramatic unless I saw a need. As always with chickens just be flexible and don't worry too much about solving a problem until you know you have a problem.
