Responsive Image "Opacity" is not working? (background image)

Setting background image responsive properties.

When I set the image opacity different for each breakpoint (e.g. tablet, desktop and mobile) it defaults to all the same e.g. the same opacity for each device?

I would of thought the image opacity should be able to be set responsively as a mobile device generally has the image behind the text whereas the tablet and desktop tend to have image on one side and text on the other (therefore image opacity is not such an issue)…