I've filed a bugtracker for the issue. The view angle depending blind spot works basically. The only thing I couldn't get to work is to take the orientation into account, as with the eye-patch carrying ai.
The issue is that the unrotated fov isn't always pointing forward for all ai (whoever thought that would be clever ). It does so for humans, but it points downwards for spiders for example. I've tried to figure out a way to get the required info from the data available, but thus far no luck. I am not sure whether it is a real issue though, as the only usecase is the eye-patch gui. If those have a symmetrical blind spot the world would probably not stop turning.
The 30 degree cone one get by standard ai is actually big enough. It easely allows you to get close up to 40 doom units to the ai, if not closer (blackjacking distance is 56, pickpocketing is 40).