9.6 KNO3 + C12H22O11 --> 4.8 K2CO3 + 7.2 CO2 + 11 H2O + 4.8 N2 (approx.)
So, 970g KNO3 and 342g sucrose, which is 74% KNO3 and 26% sucrose. This produces 662g of potassium carbonate. And, as you know, in a well made (ie, intimately mixed) LE of this type there is little slag or "pearling" left after combustion. Meaning that all 662g of potassium carbonate is dispersed as smoke (well, and droplets flung about, but largely as smoke). In other words, 50% of the mass of the charge ends up as smoke.
Increasing the amount of fuel decreases the %age of KNO3, therefore decreasing the amount of K2CO3 that can be made, reducing the max possible amount of smoke. Also, burning will be less vigorous, so it will be less well dispersed.
I think the idea to use sub-optimal amounts of oxidiser came from the common belief that "incomplete combustion produces smoke", which is not always the case...
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