partial shade is generally best. I have a variety called 'Georgia Peach' which is thriving beautifully in almost full shade.

My golden Heuchera Caramel says partial shade on label. RHS says on Marmalde l which is reddish gold....sun or partial shade. Both are out in full sun. If marmalade proves not to like full sun, it could sample dappled shade, as both plants are still in pots. Go by label, if there is one or bend it a bit.

I have 5 (caramel, lime rickey, obsidian and a couple of others whose names I have forgotten) in a very shady north east facing bed. They are next to a huge shrub and probably get a maximum of 2 hours in the morning at the height of summer and they are all doing really well. I moved them all from a much sunnier bed where they seemed to be really suffering. They are all currently l standing bolt upright and the leaves are in much better condition, whereas last year they were developing burn marks where they were being fried in the sun. I suggest you move the unhappy ones asap and watch them flourish as I did. Good luck!