I have an LHGG which has the same central square antenna as the SXT but doesn’t have the arrowed antenna of the SXT. The LHGG is OK with B20 where there is line of sight but useless where there isn’t. The SXT gets a usable signal even with no line of sight leading me to suspect that the arrowed antenna are making the difference.
I hadn’t considered that they could be reflectors, although the way that they are connected, earthed at one end with the centre tracking to the antenna feed, makes me doubt this.