Host camera view changes when others enter the meeting

Hi,

I am using a virtual background with a green screen. With one of my licensed accounts I have a problem with the camera view changing when the participants enter. I have it set up in advance so that the students can just see me with the virtual background. But then when other participants enter,  the camera view switches to a wider version so that everyone can see the area on the right and left of my green screen. This happens even when I click on original ratio. The participants 16:9 seems to override my 4:3. How can I get the camera view to stay in the original ratio, regardless of what the participants have?

Oddly enough, I have another account and when I use that account, I don`t have this problem. The camera view stays the same. However, I can`t find any settings that are different! I would be very happy if someone could help me because the view changing is not very professional. I have actually had to stop using the virtual background with this account because of this issue.