button spacing changes based on different aspect ratio of display

I'm complete noob so explain accordingly. thank you.

I have evenly spaced 6 buttons in 16:9 aspect ratio display, but when I switch to 18:9 aspect ratio display, last(bottom most) button gets completely thrown out of the main camera. if I anchor last button to bottom of canvas, spacing between buttons gets distorted. how can I change space between buttons evenly with screen height?