The shulchan aruch says that if one finishes shmoneh esrei and has to take 3 steps back, one shouldn’t take those 3 steps back if someone is still davening behind. Does this apply even if one is within 4 amos of the person already? Is the issur of walking in front of a person who is davening only if one is outside of the 4 amos or even if one is within the 4 amos?
Two rationales are given for the prohibition of taking steps back when somebody is davening behind. According to the rationale that the person behind will be distracted from his prayer, the fact that one is already within the 4 amos would not make a difference. According to the rationale of entering a person’s 4 amos, it can be suggested that there would be no prohibition for someone who is already within the 4 amos. Yet, the wording of Shulchan Aruch (102:5) suggests that this distinction is not made, and Mishnah Berurah (102:20) writes explicitly that one may not step back whether both when this would mean entering the other’s 4 amos, and even when one is already within the 4 amos. This would imply that even when one is already within a person’s 4 amos, the prohibition of crossing his path applies.
An interesting question would be whether it is permitted for somebody who is withing 4 amos of somebody davening to take three steps in a direction away from the person davening. I have not found an explicit ruling for this question.