LED Wall - Incorrect Resolution with HDMI video source showing on LED Wall
If you are seeing video that's too small on the LED Board even though you have the Streamdeck set to 100% (or full size), AND your video source is HDMI, then the issue is probably an EDID problem.
If you are using an HDMI splitter, this is a common issue. Simply disconnect the HDMI cable from the splitter and plug directly into your LED Wall input to resolve.