Why is the single-use G78G not higher impulse, then? That motor's thrust curve seems to indicate a BATES grain, as do the diagrams in the instructions, and Mojave Green is high-density and fairly high specific impulse. Even so, it only has 110 Ns versus the 130 of the G80T. (Speaking of which, the first thrust curve of the G78G on thrustcurve.org is actually that of the G80T)
Aside from that, it reminds me that Aerotech posted a picture of a highly progressive thrust curve a while back. I wonder if one of these corresponds to that thrust curve: a single grain a good deal longer than a standard BATES motor. It would be like a baby G138! Fun in a minimum diameter...