Insulating edge of concrete roof slab behind fascia

[Stevejones1967]

Hi, I need some advice on insulating the sides/thickness of concrete roof slab to avoid thermal bridging. I am shortly having a warm roof construction done on a flat concrete roof using a VPM, 120mm insulation boards, 18mm Osb boards and finished off with fibreglass. The problem is that the concrete roof sits on top of the brickwork overhanging it by approx 2” with plastic fascia fixed directly onto this. Obviously after the roof build up I am having to have deeper fascia fitted but would like to know the best way to insulate the face/thickness of concrete roof where it hangs over the brickwork to avoid thermal bridging. Was thinking about 20mm exterior insulation board cut down to size. Would this work and if so what would be the best way to fix it to the concrete and also what would be the best way to fix the plastic fascia to the insulation board/concrete afterwards. Any help would be greatly appreciated.