In daylight hours, 1090 even misses part of the eastern part of SD county. ...
At my location in the east county suburbs (south of El Cajon, east of La Mesa, immediately north of Rancho San Diego - SSE of 32°46'N 116°57'W), XEPRS is only a few dB stronger than 1070-KNX. By my standards it's definitely good enough, and I'd still listen even if it was a lot weaker. (I sometimes listen to 1110 KDIS, which is, I'd estimate, probably about 25 dB weaker.) On an "average" radio, XEPRS has a little perceivable background hiss, but I don't call it objectionable.
Even so, XEPRS is, I'd presume, below David's "magical" 10 mV/m threshold - I'd guess maybe around 5-6 mV/m or so. Maybe in an environment like where I am, where the noise level isn't all that high (signals around 25-50 µV/m, possibly lower, can be DX'ed with a decent radio/antenna and patience), XEPRS might be acceptable for non-DXers listening, but I'm guessing I'm on the edge of their "non-DXer-usable" coverage area. Also, XEPRS's background hiss can easily become foreground noise even with a minor electrical disturbance nearby.
When the Padres were also on 105.7, because of my location on the wrong side of a cluster of hills, XEPRS was still a better signal.
Also 1700-XEPE is a comparable signal to XEPRS, although it may be slightly better in the daytime. At night, it seems a little more prone to skywave/groundwave fading, at least a little more than XEPRS.
As for 94.9, their signal isn't as good here as XEPRS. If I went maybe a quarter mile away from home up the hill, I'm pretty sure 94.9 would be considerably better.