Yes there are 6 bars. Mine normally statys between 3-4. IMA assist varies with battery charge- more charge = more frequent, and earlier assist. The 6th bar will come on after a LOT of recharging- a lot of braking from speed.

IMA asist comes on to varying degrees, as you found out. Battery charge state, how hard you accelerate, how much incline, whether there is enough engine power (3 vs 6cyl) in that condition and gear. You can get IMA assist in 3cyl mode, if you are very gentle on the pedal or its a very gentle incline- if the computer thinks the IMA cannot handle, it goes straight to 6cyl.

Each generation of IMA is a little different- Insight vs Civic vs HAH. They get to play with keeping it in lean burn, we get to play with 3cyl mode. Perhaps someday there will be user-selectable preferences for how/when IMA comes on.