The obligatory precaution is that between the place where a follower performs sajdah and the imam stands, there must not be a gap of more than a person’s largest normal step.[2] The same applies with regard to a follower who is linked to the imam by another follower in front of him.
And the recommended precaution is that between the place where a follower stands and the place where another follower stands in front of him, there should not be a gap of more than the space needed for a person to perform sajdah.