eyes_out_of_frame wouldn't work for characters who don't have eyes though, like xenomorphs.
there's also cases where only one eye is out of frame like post #2604841 , or only one eye is partially out of frame like post #2365989.
i kind of agree that the name head_out_of_frame
isn't the most intuitive, but consider that the more general tag out_of_frame also means 'partiallly-out-of-frame'.
i don't see this minor naming discrepancy as a big enough problem to try and redefine the tag -- consider that you'd have to go through the 11K posts and validate their *_out_of_frame
usage.
according to the wiki, head_out_of_frame has meant fully-or-partially out-of-frame for at least the past 10 years.