The flyback we use can't generate enough power to make multi sparks.
The transformer is much to small to load the capacitor between two sparks.
A other isue will be the pressure into the cilinder from this small engines.
Into the cilinder you have ~6 bar and need about 30 mJ to generate a small spark.
If tested outside the cilinder you have a spark, but not when the engine runs.
So you wast power for the next real spark you want to have.....not good.

At high rpm the time to load the capacitor will again shorter, less power to load the capacitor.
The flyback don't have enough time and power to load the capacitor.
Thats why you can't run high rpm with the multispark option.

Use multi spark with low rpm at start, it don't do any thing......next spark will be after TDC.
All petrol wat is not burn is allready find the way out, why do we want to ignite this petrol ?

It isn't I don't like multi spark, but when you lost power (get small spark) it's better not to use multi spark for small engines.