Not sure whether it's by design and S75s were flying this way or happened due to the number of addons used in a mission, but....
I was feeling like being able to almost touch them and put them into the plane's inventory. They were clearly out of energy, flying slow (300-350kph maybe) and apparently unable to maneuver but weren't losing altitude tho. I found myself in similar situations multiple times (either in the form of SAMs parade or being chased by multiple S75s that later detonated on my six, way behind). It always happens whenever several SAMs have been launched in short succession, in this case there were 5 already launched and 2 more were locking on me. The parade was so distracting I blame it for being shot down a second later by another "pole". Maybe it was NVA's head fake by any chance? ;-)