Looking at the target cone as a 3D object that can have variable levels of transparency has me thinking of ways to create something that looks like a working radar screen.
Start with a four part model:
A light green mostly transparent sphere.
A light green rod slightly shorter than the diameter of the sphere that is a little less transparent than the sphere.
A brighter green opaque dot slightly larger than the rod diameter on the end of the rod that will point away from the target.
A darker green opaque dot the same diameter as the rod on the end of the rod that will point at the target.
As the target cone moves the line and dots will point at the target within the sphere that will appear as a transparent green circle on the screen.
The line will be the longest when you are looking exactly 90 degrees off axis from the target.
The line will shorten as you line up more directly with the target.
Looking directly away from the target the image will appear as a bright green halo around the darker green dot highlighting your course error and warning that they are now on your six.
When you are looking directly at the target the image will appear as a bright green dot in the center of the scope.
Simulated images with the target ahead and up to the right, directly behind, and directly in front of the player.