The setting that works best for most TVs is:
externalScreen.overscanCompensation = UIScreenOverscanCompensationInsetBounds | UIScreenOverscanCompensationInsetApplicationFrame; // this is the same as setting it to 3
Just setting it to UIScreenOverscanCompensationInsetApplicationFrame can cause misalignment of the UIWindow contents.
3 is a bitmask of UIScreenOverscanCompensationInsetBounds(1) and UIScreenOverscanCompensationInsetApplicationFrame(2) for those wondering where that number comes from and why it works.