Hi Bryan,
The box is a part of the slide layout generated by PowerPoint Design Ideas, it is not feasible to adjust or resize the box.
In this situation, I would suggest you check if other slide layout options generated from Design Ideas meet your requirement. You can adjust or change the picture to see if you can get more design idea options as well.
Meanwhile, if you'd like to make it is feasible to adjust the slide layout generated by Design Ideas, we kindly invite you post this idea in PowerPoint UserVoice to submit your feedback, which can help better our products and services for your and others.
Regards,
Joanne