There are two possibilities I see relating to the fixed advance magneto question(and, I'm sure, a whole lot more that I don't see). One, since Ashley fixes the issue of knock, or kickback on startup and pulling from very low rpm, by slightly retarding the advance till it does not occur, he may not be getting the benefit of full advance at high rpm when it could be used -- yet not noticing the loss of power because it is actually slight on less than a "full house" race setup. Or maybe none of us, unless we are competing with someone down at the local red light would notice it either. Or, maybe, since the reason for large advance is the time it takes the flame front to spread, especially in a high rpm situation with the intense swirl of gasses and rapid compression in the combustion chamber, the greatly increasing intensity of the magneto spark with increasing rpm partially offsets the need for such a large advance. Perhaps to the point that the top part of a magneto advance curve would, beyond a certain degree of advance, only bring a marginal increase in power. I know the reason for advance and the dynamics within the combustion chamber are far beyond my ability to analyze just sitting here typing away with no hard experimental evidence. Considering something absurd, obviously you would need NO advance if you could instantly distribute intense spark through out the entire volume of the combustion chamber. So, stating the obvious, degree of spark advance is not something once discovered and now set in stone. But if someone actually has information about this, experimental or otherwise, I'd be very interested. Just revealing my lack of knowledge is all.
