I used to believe that was the case. Below are comments from a member that has passed. Frank tried to dumb it down for people like me so I could understand it, but I still don’t get it. Maybe you will be able to.
There are a lot of things happening every time it produces a spark, and it is hard to explain it all in terms understandable to a novice. In fact, I get some more grey hairs every time I think about it. And I have a diploma that says I am a TV repairman (Not). But to share a grey hair, when the magneto points open, electrons flow into the capacitor and the voltage across the capacitor increases with time It is mighty fast, but not instant. When the time is up, the electrons flow back out in the opposite direction in series with the coil. It is that reversal in direction that induces a spark voltage in the secondary winding. A way too big (mfd) capacitor will not charge up to as high a voltage in the time available as would a small capacitor. Also, a leaky capacitor loses energy through the leak just as a leaky bucket takes longer to fill with water.
As I tried to say, the capacitor charges up in one direction, then discharges in the opposite direction, in series with the coil. Several factors combine to affect the voltage that it charges up to. A higher charge voltage in series with the coil voltage creates a higher reverse current through the coil, which results in a higher AVAILABLE spark voltage. AVAILABLE emphasized because the actual spark voltage only rises till it jumps the plug gap. Then it’s all over till next time. In other words, the actual spark voltage is rarely the maximum it can produce. BUT if it it cannot produce enough to jump the gap reliably, you get no-start, hard start, missing, etc etc.
A "Boathouse Repair" is one thats done without having tools or the skills to do it properly.