Good going. Looks like you tried for the optimim. Of course your split voltage ratings also vary from equal voltage each when stacking capacitors. Optimum voltage split, of course, is when both capacitors are the same value.
You need to split the capacitance equally at what the resonant capacitance combo will be, and if reasonably calculated still gives some vernier action of the variable cap over a desired freq. range.
So it's a compromise between loss of vernier action with too large or to small a series fixed cap and loss of a decent voltage split whereby one cap is still going to see most of the voltage anyway . Many mysterious arcs have occurred this way.
Mmm, same thing three ways just as muffled said I.
