The soil you picked for the delosperma could also have the benefit of sand /pea gravel mix as the hens and chicks have similar soil needs as delosperma.
Before planting the hens and chicks in sunny spot keep in mind where they were before so that you don't put plants that were might have been in a milder exposure to a more extreme exposure. Just suggesting to be cautious as some of us here have fried our succulents because we did not acclimate them before putting out in hot dry sun.
If I remember right, cooperi is a large delo with wide growing pattern that may overrun the semsps in due time depending on how big the semps will get. One approach is to put the semps on a slight mound so that they can be above the delosperma and not get overrun by it.