Sound is definitely a factor, despite that paper cited in the OP.
Wider bullets going just as fast as lighter bullets are going to be louder in that more air is being moved by them. Think difference between 5.56 vs 7.62 bullet snap is real, 5.56 vs .50 cal is more real, but a better example is the sound a standard artillery round flying overhead (at ballistic velocity) vs a 16" battleship or railgun round passing overhead. A very noticeable difference of sound, based on air being pushed out of the way by a supersonic projectile flying overhead.
Suppression is largely a psychological event. For bullets, the louder the snap, the more potential it has to increase what one paper I read called the Perceived Probability of Incapacitation (psychological), versus the more straightforward Probability of Incapacitation (quantifiable). Louder means more danger, it means either closer shots (the enemy might have located your exact position), or it means deadlier incoming round.
I read some small blurbs from Tony Williams about suppression distances by sound, by weapon, (though I have no idea where he sourced it from), but from my own personal experiences in Iraq, having been shot at with light weapons and heavy, it was rather easy to know which one was the DShK vs the AK, and that I feared the DShK incoming fire more than an AK. Not only on its abilities to hit me (iron sighted AK fire at long range with an Arab pulling the trigger wasn't exactly something scary), but knowing that a lot of what I might be using for cover against 14.5 HMG incoming AP round might only be turn my cover into concealment. Thus increasing fear factor to the point that the fire very well (and did) ground me, thereby suppressing me.
So I'd say the lesson is that sound matters, to get better sound, increase the lethality of the incoming round, make it close to the target (accuracy), and make it repeated (volume). Of course it would vary by situation, training, motivation, leadership, morale, but all things equal, the louder the snap, the closer it is, the more of them there are, the better the suppression effect.
Here is a good article on the acoustics of small arms suppression. I don't know if I buy everything written, but some very interesting points are brought up.
The Real Role of Small Arms in Combat
Also, since you appear to actually like this subject, here is a link for a Vietnam study on suppression done in the form of survey results to infantryman:
The Identification of Objective Relationships Between Small Arms Fire Characteristics and Effectiveness of Suppressing Fire
