“There’s a halacha in the SH”A that a man is required to walk in the street with his head bent so low that he can see at the most, 4 amos in front of him.”
That’s not how I’d translate “lo yeileich b’komah z’kufah.”
There is an idea brought down, not necessarily in the Shulchan Aruch, not to look outside of one’s “daled amos,” but I’ve never heard that one’s posture should make it impossible to do so.