When you insert a Live Content slide into PowerPoint for poll results, your PowerPoint theme is ignored when you open those slides in Slideshow mode. Even if you attempt to re-size the box that appears on a Live Content slide, the change is ignored and poll results fill the entire screen or window.
It is possible to re-size the overlay for PowerPoint. By re-sizing the overlay that holds poll results, you can then potentially show other images or content on the projected screen with the poll results. The brief video below will demonstrate that process. Written directions are also available (attached).
The following video also refers to an article entitled How to Customize Poll Result Slides with Background Graphics.