For ultrawide displays, add a 30% / 40% / 30% third option.

[vincentg37]

To maximize centered window on an ultrawide display, consider allowing the option to adjust the ratio of thirds, such as 30/40/30%, for example.

[rxhanson]

Rectangle is intentionally slim to keep it more simple and approachable. I don't have plans to add these in myself, but I would consider a good pull request that adds them in as terminal command configurations (not in the UI).

As an alternative, these can easily be configured in Rectangle Pro (paid) in the custom size/position tab:

[vincentg37]

thank for your reply