The Featured Image for any post would only replace the header image if the size of that featured image is greater than or equal to 900 x 198 pixels. Images smaller than that will not replace the header image when the post is displayed.
This free Support Forum relies on contributions from our support staffs and fellow Graphene themes users. While we endeavour to provide adequate and timely support, due to its voluntary nature responses are not guaranteed and may be delayed.
If you require urgent assistance, you may like to consider our Priority Support option.