AKA: "Wide Youtube", AKA: "Wide video container" - Uses the page space on youtube more efficiently (especially good for high resolutions)
< Feedback op Space-efficient Youtube
I think it's not actually limited to 4 per row technically. YT (not my script) scales it depending on the space available. It does seem to cap at 6 per row though. (You can test this by zooming in and out in the browser: CTRL + Scroll wheel)
The video containers have gotten larger though (I think?). There currently is no option to adjust the containers in that section. I might add that option and otherwise see what I can do to improve that page later.
Youtube has recently fucked things up again, and so videos pages on channels are 4 videos a row. If you could fix this (when the change shows up on your end, if it hasn't already, more A/B testing bs I believe) that'd be superb.