Extract of style.css, showing an untested example of how you might adjust the mobile logo size (and space around it) on Kickstart Pro

style.css

@media only screen and (max-width: 900px) {
	.header-image .site-title a {
	    min-height: 95px; /* You need to allow more space for the logo if you're doing this so increase the min-height to suit */
	}	
	
  .header-image .site-header .wrap {
      /* background-size: 93px 48px;*/ /* Removes image resizing completely, otherwise you can uncomment it and adjust the size manually by changing the values (making sure to keep it in proportion to the original image */
  }
}