Bands not drawn above and below

Sometimes DALLE 3 generates 1792x1024 images with uncolored bands both at the top and below the image. In this way the image is less rectangular and I’m fine with this also because I’m generating images for publications and therefore I’m fine with them not being too rectangular but that, thanks to these 2 bands above and below, the image is closer to a square. What could you write in the prompt to always generate, and not randomly, these uncolored mandas above and below?