This might be a weird thought, but the god Crom Cruach of Ireland, might it actually be a Magical Locus Genii in charge of the local region’s fertility?
Perhaps the earliest inhabitants of the Emerald Isle worked out a crude way to direct it. 12 standing stones to give an Astrological binding, and then surrounding it with fertiliser to tweak how much fertitlity it distributes. Extra fertiliser means it can afford to be extra fertile. and blood and bone fertiliser is very effective.
Of course, all this focused human vitality would have caused at least one faerie to take on the role of “Crom Cruach”, but the Genius Locii might be offended by faeries when excessive human activity brings the faeries to the spirit’s attention. At which point the spirit might slaughter an army in front of the spirit feeding vitality to the faerie imposter.
Until St Patrick comes along and returns the Genius Locci to the Earth. Leaving the Faerie imposter freer reign.