When Patch CTF is performed on mics with gold film in one corner (or other high contrast junk elsewhere in the frame), it gives results that are probably not useful, e.g. see below.
Two possibilities for enhancements to avoid such a case:
Allow the user to set a defocus variability threshold, which if exceeded during Patch CTF, forces it to revert to whole frame fitting.
Perform some kind of image segmentation prior to CTF fitting (this would also be useful for picking) and don’t use patches which include gold or high contrast junk.