To find a sensible RCD combination, it's a tradeoff as to what amount of energy comes from the transformer primary as it shuts off, versus what voltage you wish to accumulate on the capacitor, versus the watt rating of the resistor.
The formulas take energy from the transformer, and convert it to energy stored in the capacitor. I believe the formulas have units of joules on one side of the equation.
We might speculate that if you have 1 Henry carrying 1 Ampere, it is the same energy as 1 Farad charged to 1 Volt. However the calculation is not linear. It is not the same energy as 1uF charged to 1 million volts.