infiniteX2P 7.0.6 will be released on the App Store soon to address an issue where window controls being out of place when Extended Input Area is enabled. The picture below is after fix. Prior to infiniteX2P 7.0.6, window control on the external display would be on the far left.

This also takes corner radius of the iPhones into account. All buttons should now be reachable. I hope iPhones doesn't get more rounded in the future.