All devices will work better if they are in direct range of the controller - that’s not to say that they will necessarily work badly if they aren’t in direct range of the controller.
How well the network works will be dependant on a number of things. Firstly, how many devices are in the network - the more mains devices the better since these will route frames to devices that can’t hear each-other directly. So, you need to make sure you have enough routing devices in the network - this can be a problem when starting out since most people don’t fit everything in one go…
Other factors such as building material (wood, concrete etc) will influence coverage.
If you can put your controller in the middle of the house, it’s almost bound to be better than at the extreme of the network. In my case, it’s also at one end of the house (single story, but quite long) and the system works well even through only a couple of devices can directly communicate with the controller.
The only thing I can add to @chris’s post is that in my setup I had only one mains powered device that could see the controller and the network did not work well at all. However, I added a second one and now my network is rock solid. So if you have around a dozen devices make sure there are at least two mains powered devices that can see your controller and most of the other nodes. In my case I added a repeater.
Another approach could be to put your controller on a board computer (Raspberry Pi, BeagleBone, etc) in the center of your house and use socat (Linux only I think) to get that serial connection to your OH server in the basement. Others have reported being successful with this sort of setup, though it assumes good network coverage.
A USB cable must be no longer than 16.5’ / 5 M though closer to 10’ / 3M is the more practical limit.
Being up high is not necessarily going to provide you better coverage. My controller is on the top floor of a two story with a basement house. The bulk of my devices are on the main floor and every device is a neighbor of every other device (except the controller). In this configuration the only device that could see the controller was the one directly underneath it. I added the repeater on the top floor directly over an other device to give everything two paths to the controller and it works great.
The end lesson here is that you will probably have to experiment with your own deployment. Keep an eye on your network map in Habmin and make sure as many mains powered devices are neighbors of the controller as possible and you should be fine.