header image size

Hi. First congrats for this wonderful theme. I was browsing the web and trying different themes but all were kinda unusable with the possible settings in the free versions. Yours is great to set in certain limits. Once I need more options I definitely will go with your Pro version. There is only one simple thing I need to get confirmed regarding the header image size which is suggested to be 1670x720 px. Since I have a picture that I want to use as the header image which is 1670 px wide but only 500 high, could be there a problem with the visibility of the header image under certain circumstances like cropped width of the image or "open" space with background color? With other words ... is there a mandatory image proportion? Thank you.