With a 60-40 ratio, both panels are usable. And more height gives you an overview of the conversation while it doesn't cost anything since the extra width that's otherwise dedicated to titles is superfluous.
But how much does saidit use? Tiny. How much does voat use? Super tiny. Matrix is in between both of them. It's important to remember that it's a link site with a chat feature. I am realizing I can get more height out of it though and make the height more responsive to the screen size to make sure it doesn't load overflowed on smaller screens.
The size is configurable on Saidit, I've increased it to 40% there. The thing is that the default size just isn't very usable while the extra width for links doesn't seem very important to begin with. I've implemented chat on Rabbit Hole as one big box at the top btw, that's how much screen estate I'm willing to dedicate to it.
I use several monitors, some landscape (video), some portrait (chat), all standard 1920x1080p - like many phones. For both video and chat I employ separate dedicated tabs over using a sidebox.
I am realizing I can get more height out of it though and make the height more responsive to the screen size to make sure it doesn't load overflowed on smaller screens.