To close this off, the R seems to have a unique armrest layout. The rear part is a single cover that can be levered off using trim tools. But it is not necessary to do this. The main two screws are under the forward horizontal part of the armrest. From above you can lever the top of this part towards the centre of the car, and then remove it. This exposes the main plastic moulding that takes the load when closing the door and or leaning on it. The two screws are accessible down obvious tubes in the moulding.
I was surprised how much leverage it took and felt certain I was going to break something, but the trim tools (5 plastic levers of various shapes, available on ebay for a few pounds) spread the load and it all came apart and went back together again with no marking or other damage to the trim. I don't recommend trying it with screw drivers etc. unless you know exactly where to apply pressure.