Code completion doesn't work with filepath variable

I'm working under such directory structure as below:

/src/assets/css/main.scss
/src/assets/imgs/bg.png

"/src" is marked as "Resource Root".

Let's say I'd like to set bg.png as background image of body element.
After typing "url(/a", path completion appears as below.

Next, I declare a scss variable which indicates filepath to imgs directory such as this:

$imgPath: "/assets/imgs/";

Under this condition, path completion doesn't work. See the screenshot below. After typing "#{$imgPath}", I expected to appear suggestion(completion) popup such as "bg.png", but in vain.

Is there any way to activate code completion with scss variablized filepath?