At present at least 1080x1980 resolution image is required for a full screen image in a campaign(in-app message), which increase the size of the image and increases latency in loading the image. Smaller images are show scaled down. Instead the scaling should be done to fill the entire area. Or there must be an option to upload multiple images of different resolutions which can be used on different screen sizes devices. I've attached the screen shot of a campaign with smaller image.