Info on image layout and responsiveness for ipad and mobile

Hi. I have bought Unicon theme which is great but am having real issue working with responsiveness.
Firstly I upgraded to Visual Composer to version 5 since the version which came with the theme 4.5 did not offer the VC responsive options. I disabled line 20 of functions.php to enable the responsive options in VC.
However I am just not understanding how the whole responsive thing works in VC or Unicon.
Please have a look at http://jacquelinemajer.com.au/ on mobile or ipad
on different devices the image of the lady is all over the place.
Via the VC responsive options I can see how to alter column width per device and hide elements on devices but not how to move an image or item downwards on a particular device.

What kind of responsiveness does Unicon have built in?
What image dimensions should i be using to make sure an image is aligned correctly on all devices? Is my image too small in general? Do i need to design it differently for the desktop to make it work better on mobile?

Please help me understand this because I feel I am missing the basics and getting no where and frustrated. I have looked for information related to resonsive design using VC but found very little detailed information.

Thank You
Chris

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