Hi Richard,
First of all, we have provided support logo@2x for retina display only. That means, the logo@2x will show in the retina display only, will not show in the mobile device.
In this issue, you have to use the same size logo for both logos & logo@2x. However, you could increase the resolution (not size) of logo@2x to get a clear view on retina display.
Moreover, if you want to use a big logo, then you must have to write and use custom CSS to get fit the logo on header for both desktop and responsive view.
Furthermore, please extend your support extension to get further support in the future. This is because, your 6 months FREE support was expired on 2018-02-11.
Best Regards,
ThemeLooks Support Team