I am having no success with heucheras. I live in zone7a. I've tried them in partial shade, full shade a.m. sun. But they just start looking pitiful, then dry up. Our soil here (NM) is alkaline, could that be the problem? I have an automatic watering system, so they do have moisture.
You should try looking for any of the hybrids with Sanguinea in the name. The species grows at about 6,500 feet in the granite crevices in AZ. I'm not a big fan of auto water systems when it comes to plants. Lawn no problem. These plants do not like wet feet. Good drainage is a must.
The hybrids come from a diverse family background and frankly they are an experiment when it comes to exposure. I would start with shade and move out from that. For me the light green leaves take little sun but as they get darker to the plum more sun. I just use that for exposure. Of course I live in Washington state with little sun and lots of rain. I have found that the Sanguinea are harder to grow here.
Hope this helps. If you see this book in your library or bookstore it is worth a read. Heucheras and Heucherellas by Dan Heim and Grahame Ware
Instead of using the auto water system, why not put the plants in containers with good drainage. If you are not happy with the exposure, the container is easy to move. You can place the container in the ground as well. It makes experimentation easy.
I use oversize containers, often with multiple plants and drill extra holes where necessary.
I have better luck with them in containers. I also almost never water unless we're going into a drought period and then I don't water heavily. When I pot up I add a tiny pinch of water retaining crystals in the bottom third of the container and then backfill until I get the correct level for potting up the plants. I clean them up in the fall and winter to remove dead leaves and pieces of the plant that have gone woody and died back. Each spring I top off the soil and make sure that the crown hasn't sunk too low or heaved too high.