Planting ideas, shallow soil depth in full sun

[WobblyLondoner]

I am planting up an area 80cm by 380cm directly on top of a metal storage unit. The soil depth is 20cm. There is built in irrigation which I can control and drainage. The garden is south facing, in London, with no shade above it. As the unit is metal it gets very hot in the sun!

My planting thoughts so far are to aim for plants that would suit dry gardens (even though I have irrigation) on the grounds that they will be very exposed and likely to get very hot in the summer. I would ideally like insect attracting flowers and scent would be nice too. Because of the depth of the soil and the position of the unit, I would rather avoid anything much higher than 60cm.

My list of ideas so far includes:

Rosemary prostratus (like the idea of this trailing but am concerned about Rosemary beetle which saw off a previous Rosemary).
Thyme
Saxifraga London pride group
Euphorbia myrsinities
Erigeron karvinskianus & four winds
Echinacea (smaller ones - possibly too big given depth?)
Eryngunium bourgati (possibly too big given soil depth?)
Nerine
Salvia sylvestris Blauhugel
Armenia
Geranium ballerina
Sedum spurium ‘tricolor’

Any thoughts very welcome oh wise fellow gardeners..

Cistus
Helianthemum (rock rose)
Lavender
Nepeta

About the only thing I can think to add to that is houseleeks.

Also, I'm just wondering if any cyclamen might work ... although we often see them in quite shady locations under trees etc, I was surprised to see a lot on dry looking slopes in Greece in October. I've got some self seeded into a barren stony area between a house and a wall.

I think the heat from the metal storage unit is going to be a problem, it might be a bit like trying to grow plants on a cooker!

Sempervivums might work, as they do happily live on roofs which can get very hot.

Not Cyclamen, though, they might be alpine plants but generally prefer some cool shade.

It may be specific species of cyclamen, ones which are dormant in summer.

Thanks all, that's helpful and some good suggestions here. The heat point is a good one and suspect does rule out the cyclamen, love them though I do.

Persicaria does ok in shallow soil.