Zooms to the top instead to center or bottom

[leolux]

Stellar zooms my background-image always to the top of the image instead to the center when the image gets smaller than the width of the screen.

It seems useless to set the css property background-position: center center; for the background-image because it will be overriden by Stellar. And adding the "!important" word results in no parallax effect at all.

Here is my configuration:

$(document).on('ready', function () {
    $.stellar({
      responsive: false,
      verticalOffset: 60,
      parallaxBackgrounds: true,
      parallaxElements: true,
      horizontalScrolling: false,
      hideDistantElements: false,
      scrollProperty: 'scroll'
    });
  ...

So how to tell Stellar to zoom into the center instead of the top?