Well, my first suggestion would be to add some brighter colors to the posts. Only because it doesn’t really catch my eye. Not only that, but do you have different colors for different categories or the option to change the color?
Clicking on a blank space in the calendar view open the current mini calendar popup offering to add a new post (great to progressively convert it in an editorial companion) The idea can be also useful in some way to the mini calendar popup when there is a scheduled post
