It’s done to match the screen size. But if you want to adjust then you can increase the padding of the text area on the slider image. You can add the following CSS in the “Appearance => Customize => Additional CSS” box:

/* Header Padding for Screensize 1360px and above */
@media screen and (min-width: 85em) {
  .custom-header-content,
  #feature-slider .entry-container {
    padding-top: 450px;
    padding-bottom: 450px;
  }
}

Regards,
Sakin