What is the chiddush that Rav Ashi tells us that he did not hear the teaching of Rabba Bar Rav Huna yet he intuitively also knew that he should say the three reminders בניחותא?
Maharsha (in the parallel sugya in Gittin 7a) explains that there are potentially two reasons one would speak softly. One is that he has a better chance of convincing others to listen to him than by screaming, and the second is that there is an inherent value to speak this way. Rabba Bar Rav Huna instructed us to talk to this way to prevent kilkul in these three items (i.e. to convince others to listen) but Rav Ashi was saying that even when your purpose is not convincing, one should be talking this way, and that is what he meant when said that מסברא he would speak this way.
Cute Vort on this idea is said by the Ben Yehoyada, on the pasuk דברי חכמים בנחת נשמעים that נחת stands for נר and חלה (the question of עשרתם) and תחומין.