If your "Series resistance" is zero, then DF1 and DF2 are just the same as your values for "Dissipation factors (%) at f1 and f2 [DF1 DF2]". If the resistance is non-zero, then we have to make a correction to account for the series resistance. In that case, you have a resistor in series with a nonlinear resistance. The dissipation due to a series resistor (by itself) is simply 2*pi*f*R*C. If we write the complex impedance for the Debye equations, then the real part will be R plus a term related to the permittivity.
To make things easier to unravel, I would suggest setting the series resistance to 0 in the capacitor block and use an external series resistor if you really need it. Then, the DF for the capacitor will be exactly what you input to the block and it should be easier to figure out.
