I'm not surprised you put a smiley on, Kev, I bet thats great to see - never realised you could get a group of blackbirds together like that! I'd love to see a picture of them (hint, hint).................
My male blackbird and the 'baby blackbird who lives under the hedge' are both sunworshippers too. Adult B just lays on the lawn, wings and tail extended. Baby B has a technique more like a lizard - he stretches out one part at a time. But as you say they stay completely still for (what seems like) ages. And numpty here (me) gets worried about them and feels compelled to stay and watch them till they've finished so that bad 'nature' doens't get them!
Don't forget the photo, Kev!