I actually stumbled upon a great blog! I was looking for information about the size requirements of images for Modern SharePoint News. Sometimes, actually most of the time, the images are aligned properly or just look bad within the News Web Part. The following blogs provides a great explanation about the topic:
http://straightenthemaze.com/2018/02/21/how-sharepoint-handles-images/
Big time props to Beth Hall from Straighten the Maze. Cool name 😀
