@Iain Beveridge - There is no way to do this using native Miro functionality. And if there is, I couldn’t figure it out. I also had a quick glance at the Video Chat Help Center article and saw no mention of resizing the video bubble.

You could always force the browser size to be larger by using the browser zoom, but do this knowing it may have unexpected impacts to other Miro functionality.

By the way, there’s already a Wish List item - Full Screen Video Chat - feel free to upvote it and describe your use case. 

Thanks Robert... Shame… the ability to even double their size would really aid communication. I appreciate the aim is to engender collaboration ‘on the board’ - but sometimes the video call becomes more important. Here’s hoping!