You got the wrong idea, VK. You don't need a prop like you have here to show the volume. You just need something in the scene.. anything. Volume will show up against any object in your scene, including your model's face and body.

For this scene, I would just put a backdrop behind your figure. Don't put anything in front of her face.

Just like in the other thread you raised on this subject... a light, a backdrop, and the Atmosphere setting.

(edit) xpost with markschum... he's more succinct than me!

"If I were a shadow, I know I wouldn't like to be half of what I should be."
Mr Otsuka, the old black tomcat in Kafka on the Shore (Haruki Murakami)