If you don't have the Energi model, you simply don't have the battery power required to do any better. Your smaller battery not only means you can't drive very far on electric alone, but there's also a limit on the peak power it can output.
It sounds like you're trying to drive around using electric power as much as possible for maximum MPGs, which is actually not what you want to do in most situations. This video is for a Prius, but the concepts are the same. Usually, the best way to drive is like you're hypermiling a normal car, except you don't have to manually start and stop the engine when coasting or stopped. Electric power is used mostly for slow speed driving like parking lots and for helping to extend coasts/keep traffic happy. I generally accelerate kind of quick in my Prius in order to use the gas engine for what it's most efficient at, high loads.