The regular product model improves upon its individual grammars more than the ST-Prod-Mult product does in the later SM rounds, as illustrated by the relative error reduction curves in figures 2(a) and (b).
the product of the SM7 regular grammars gains a remarkable 2.1% absolute improvement over the average performance of the individual regular SM7 grammars and 0.2% absolute over the product of the regular SM6 grammars, despite the fact that the individual regular SM7 grammars perform worse than the SM6 grammars.