Answer: Your image sounds great! In my experience these two campanulas do better with a rich soil that is evenly moist and yet well drained and has had ample organic matter worked into it. They do well in partial shade but need more shade if the soil tends to be drier. If your rock is in a sunnier location you might try the annual ageratum in several shades of blue, or for perennials you might consider the blue flowered vinca minor or perhaps the blue flowered ceratostigma plumbaginoides, or perhaps a veronica such as "Goodness Grows."
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