You are using the wrong technical terms. Spill is part of the light that has already exited the flashlight. The term has no meaning inside the light. It only pertains to lights that have a normal, front-facing reflector (spill is the light that doesn’t hit such a normal reflector, it directly exits the flashlight).

The collar only works because the phosphor of the LED is excited additionally by redirected blue light. The phosphor is not a mirror, it doesn’t reflect a lot of light.

The Wavien collar collects 75% of the total amount of light that a domeless LED emits. The blue part of this 75% re-exites the Phosphor which doubles the Luminance. Thus the 25% of the total light that directly exits the collar (and can then hit a lens) is effectively doubled.

This means the collar is around 50% efficient in terms of lumens (total amount of light).

To understand how it works you need to understand what Luminance is/means.