I do have some red Astilbes (variety unknown) that take the direct sun like troopers. They get several hours of hot afternoon sun. They are planted in a bed where an oak stump was ground up about 3 years ago. The oak chips were spread out and not concentrated in one spot and I mulch with shredded leaves. The foliage has grown very thick so the ground is totally shaded, maybe keeping their roots a lot cooler. They get some supplemental city water via the sprinkler if it hasn't rained for a couple of weeks. I've actually had to thin out some plants. I think maybe pure luck here.
