I'm trying the soil type as above reading:
"Unlike many rock plants, lithodora needs a humus-rich soil, rather than a gritty one, so make a special planting pocket for them. Place several rocks close to the plant so the soil underneath remains cool and moist in a hot summer, giving the roots a reliable comfort zone."
as I'm planting in a narrow border by pond edging, seems ideal for that place.
It would be useful to keep in touch.