The IMA system uses a small 13 hp electric motor to aide the gasoline engine. Battery capacity and electric motor are so small that the effective mpg benefit of the system is to extensively extend your coasting distance.
While coasting, gasoline flow to the engine is stopped, and mpg soars to an indicated 150 mpg. I use the energy flow screen and a light touch on the gas pedal to darken the gas icon while showing a positive flow from the battery to the car icon ( " EV Mode").
All those hills which you've become aware of can now become resources for battery charging on the down grade (lightly tap the brake pedal without slowing the car concurrent with the ASST gauge's movement toward CHG). Flat areas prior to upgrades become places to build enough momentum to get ya to the top without use / minimum use of ASST. Down grades are also great opportunities to build vehicle speed.
Check out actual Insight mpg numbers at Honda Insight MPG Reports | Fuelly
. Join the site post your numbers, make some entry's in "notes", periodicly review your notes to see what is working, and what isn't.
Cobb as well as others at this site have done a lot with mods.