On the general point , it seems that most monuments sited among hills don't reference the biggest hills , they may be in view , but there are no obvious indicators towards them i.e. entrances , outliers etc . This is even more noticeable when we consider possible astro alignments .When hills provide the horizon the astro events rarely occur on the peaks and cols/bealachs .It could be said that they are avoided , but more likely it's the case that they don't matter .
You can't beat a visual confirmation but even the various horizons show that PyF has a higher horizon from the row than the col ,but it must be just poking above . The dates for the sun rise at that spot i.e. just above the height of the col between Foel Darw and Garn Las as seen from the row are 8 October and (coincidentally ?) 5th March . It won't change too much in the next couple of days so maybe someone might manage to confirm it .
