Rav Shlomo Zalman Auerbach says that this Halacha does not apply if the person is Davening in a place where he knows that people will have to walk within 4 Amos of him (e.g. most places in a Beis Midrash, anywhere near the aisle).
Rav Shlomo Zalman supposedly used to say that if someone is blocking the aisle by Davening Shmoneh Esrei you can physically move him.
I was also once told a story by someone who was once Davening in an aisle and someone behind him started, very loudly, to say “nu, nu”. After 3 or 4 times the guy couldn’t take it anymore and turned around to shush the person who was disturbing his Shmoneh Esrei. He was mortified to find that the person he was about to shush was Rav Shlomo Zalman Auerbach!