The specification is 20dB up to 1.5GHz and 13dB up to 3GHz so it looks
to be within spec.

There are changes to the SMA connector transition in the plus4 which
brings port 2 return loss near or above 20dB, but I see significant
variations between devices (could be soldering variations), so it's hard
to tune it to be a very good match on every device. First prototype I
assembled was 25dB but later ones were 18dB, so I think a spec of 16dB
may be achievable. You can always add an attenuator (5 or 6dB) to
improve port matching.