Changing header size on Twenty Thirteen theme

I am trying to insert a 2000×784 px image as a header on the Twenty Thirteen theme.

I’ve gone through the steps in the following thread:

https://www.ads-software.com/support/topic/massive-headers?replies=18

It seems that the header image import/cropping interface on Appearance>Header is overriding the min-height setting I inserted in style.css.

Do I need to bypass the Header interface and insert the image directly through the non-child Twenty Thirteen style.css?

[Moderator Note: No bumping. If it’s that urgent, consider hiring someone.]