Flocking/ Boids Algorithm: Field Of View in 3D

Hello. I am trying to make boids algorithm in Unity 3D.

I got into one problem: How to implement field of view in specific angle?

360 degrees is easy - U check only distance between two boids.

I would be gratefull for any ideas:(

I already tried with mesh collider which is cone but it didnt go well. - not working for 180 and higher. So I am looking best way to calculate this.