Today was the first day since the solstice that I could head out and check a sunrise alignment I've suspected for some time. No one has ever recorded a winter solstice alignment at a portal tomb (why should anyone look? They nearly all face due east.)
As I suspected the sun broke the south-westerly horizon at the lowest point. This rather nicely adds weight to my theories about horizon notches being as important, if not more important, as peaks (at least in Irish sites).