Hey, @EBailey,
Take a read through this Zoom Support article on using HD video:
https://support.zoom.us/hc/en-us/articles/207347086-Using-Group-HD-video
Note especially the section "How to send and receive Group HD with the Zoom client", where it states that the video sender and receiver both must be in full-screen mode. Look at the Zoom Settings Statistics panel under the Video tab to see what size video is being received/transmitted. Note that the resolution will vary depending on the size of the window; it doesn't look to me like full-screen mode is a requirement, but the Zoom app is smart enough to know when it doesn't need to receive a high-resolution image, and down-scales the incoming video.