**I would anchor the rail into the concrete, using a fixing arrangement designed to bridge the roughly 70 mm of plaster and insulation.** I would not rely on cavity anchors in the 10 mm plaster facing without explicit approval from the lining manufacturer for loaded wall cabinets. The French specification link hasn’t come through, so I cannot check that particular board.

The important issue is the complete load path:

- **Cavity-anchor ratings are conditional.** A “20 kg” rating applies to specified board thicknesses, installation conditions and load directions. Several anchors close together can fail by breaking out a shared section of plaster; their capacities cannot simply be added.
- **Ordinary long screws into concrete leave a problem at the surface.** Tightening can crush the lining, and the unsupported screw length must resist bending as well as the cabinet’s downward load and outward pull.
- **The insulation should not serve as structural packing.** The connection needs rigid support or a rated stand-off system that transfers the loads to the concrete.

Two practical approaches are:

1. **Purpose-designed stand-off anchors.** Systems such as Fischer TherMax are made for fixing through non-load-bearing insulation into the structural wall. Their published capacities depend on stand-off distance, substrate and loading. Treat this as an example of the appropriate fixing category; the manufacturer should confirm suitability for your interior lining, sustained cabinet loads and METOD rail connection. [Fischer TherMax guidance](https://www.fischer.co.uk/en-gb/products/fixation-on-etics-insulation/fixing-in-substrate/thermax-12-and-16/stand-off-installation-thermax-12)

2. **A structural backing strip or blocks attached to the concrete.** Locally remove the lining behind the rail and install suitably designed backing extending to the finished wall plane. Attach the rail to that backing. This is more invasive, but provides a direct support arrangement. The detailing should also account for thermal and acoustic bridging.

Your concern about leverage is justified, but it does **not automatically mean enormous screws**. Proper support across the insulation thickness changes the connection substantially. The cabinet’s lower rear contact points also resist its tendency to rotate, so those points need adequate bearing support.

Ask the installer or anchor supplier to specify the **anchor type, concrete embedment, spacing, stand-off support and rail-compatible heads/washers** for the total loaded cabinet run. IKEA likewise requires fixings appropriate to the wall construction. [METOD installation guide](https://www.ikea.com/gb/en/files/pdf/68/5b/685bdadb/metod-installation-guide.pdf)

For this installation, I would accept a concrete-backed fixing detail with documented capacities—not a recommendation based solely on the cavity dowels’ “20 kg” label. Before drilling, locate reinforcement and concealed services.