I don't think the vision cone design works well for a turn based game where you can easily exploit them by dashing by 20 meters at a time when someone "looks the other way".
The cones are also far too narrow considering peripheral vision and simply looking around without turning, especially when you are alert. It should be at least 180 degrees.
And then the main thing to detect someone trying to sneak past you is NOISE, which is completely ignored in the current implementation of stealth that only accounts for a narrow tunnel vision that only turns every 6 seconds. It's absurd a Fighter in Heavy Armor doesn't even roll a check outside the vision cones and that pulls the rug under actual stealth builds.
I don't know what "fun mini game" they wanted to create with the cones, but it's not working. I would ditch the cones entirely and make two detection circles that would account for everything - sound, peripheral vision, looking around. Perhaps a shorter radius for a normal Perception check and a longer radius for a check with Disadvantage, to keep the spirit of the "mini game" intact even if the easy exploits would be removed.
