Hi Charlie, you're right......in Dutch it's easyer to explain for me.....sorry for the mistake(s) I make.
I mixup *in* and *de*, *in*creas = speedup and *de*creas =slowdown....yes ?

If the freq is speedup the coilfreq, the capacitor have a better load.
If the freq is higher, the bridge can make a better/equal DC to load the capacitor.
But you need time to load the capacitor.
If the capacitor is to big, the capacitor will not load complete between two sparks.
Only a complete loaded capacitor is given a good spark.

Maybe I must go back to school to freshup my english [8D]