Here in west Houston, WOAI is strong day and somewhat weaker at night, but always on top. I think I'm about 100 miles closer than you are to San Antonio, but a bit surprised you can't get WOAI in the daytime.
I'm ~150 miles from WOAI's tower, so would the relative weakness at night be due to cancellation at that distance?
I've heard possible Spanish under WOAI at night but have not ID'ed anything else on this frequency.