1. “spill” is light that comes out of a flashlight without hitting a forward-facing reflector. A lens flashlight has no spill regardless of whether you use a collar or not. The light hitting the inside of the head is not spill because it does not exit the lens.

2) The collar reflects light back at the LED, not at the lens.

The entire point of the wavien collar is that it does not aim any light at the lens.
This is why the lumen output can increase without making the spot larger (which is what a secondary lens does) and more lumens + same area = higher intensity

I think you simply don’t understand what the terms mean, that’s all, not your fault.