Hey Jonathan,
I’m not sure if I have your answer, but here’s what I’ve done that works. I use an image size of 1132 x 269 and made note of it for my future use. I’m not sure how I landed on those dimensions, but it seems to work everywhere.
I use Photoshop, so it’s easy (for me) to change the pixel dimensions of an image. Also, if do try this, then be sure to keep your image the same proportions. That means you can change your width to 1132 and the height will become 226. You can then increase the height of the canvas of your image to 269. The end result will be an image that is 1132 x 269 with the same proportions as your original (because we added space vertically). The Aspire theme uses a black header background, so make sure the additional space is transparent and save as a PNG.
I hope this helps you. This is what it looks like on my site: https://scottsmoneymachines.com/
Scott