Cinemachine Multiple Point Of Interest cameras

Hello, I am implementing point of interest cameras in my game where I want when I activate an event object to spawn a camera in the cinemachine mixing component and lerp the weight of that camera.

The problem is that if I have already a POI camera and both the main camera and POI camera have equal weight amounts (0.5 on both of them) , when I add a third camera the weight of them is shifted and I cannot easily control the new weight amount. My question is: is there some formula that I can use to make it work or if there is an alternative way to deal with this problem. I want to set the camera weight for example from 0(no focus) and 1(camera is focusing the target) and the camera mixer component to handle the weights