MacGillivray's Warbler?

I believe this is a MacGillivray's Warbler, winter female. At least that was the opinion of one expert birder in the Lower Rio Grande Valley where this was taken last week. Several other sightings of this species were reported on eBird that week, although not at this specific location. The bird was low to the ground but obviously not on the ground. It has some of the right characteristics (full grey hood, eye arcs); but lacks any apparent yellowish lower mandible. It is possible it is an Orange-crowned Warbler, which was also prevalent in the area, but this one looks different -- more hood, no supercilium, no streaking, shorter tail. Any thoughts? If so, please explain why it is, or isn't.