That camera group is most likely configured to be a fixed aspect ratio in Blue Iris, which disables UI3's ability to demand its own aspect ratio.In UI3, When I right click on any camera (in a group... while live view, or timeline, or clips are selected, ) and choose "Group Settings", all I see is:
View attachment 242001
I can't seem to find any place with the settings choices you talk about... someplace else?
Use Blue Iris's edit layout button, then right click in its video area and find the group-level aspect ratio control.