It is the distance from the routing layer to the first ground layer that is important. For the CC1101 standalone ref design this distance is 0.8mm. If you look at the CC1101-CC1190 ref design which uses 4 layers the distance is 0.25mm down to the first ground layer. Based on this you should be able to reduce your PCB thickness to 0.4mm without issues. When the thickness goes down to 0.2mm the parasitic caps will start to influence the performance.
A text book will only give you the theoretically equations that will give you an idea of what will happen if you go up or down on a parameter but for development (not using the ref design etc) a electromagnetic simulator like ADS should be used.