I originally set up my Livewire w/the stock motor & 1500ma 2S li-po. I mounted the battery virtically by cutting the foam right in front of the wing.
After stripping the gears in the original setup (about the 4th flight), I installed a canned 400 with a 3:1 gearbox. Performance was worse!. I finally broke down and went brushle$$. A PJS-800.
I also added an additional li-po cell. I mounted this one vertically, centered over the wing (under the canopy), again with a small slot to insert the cell slightly into the foam. My balance is still within tollerances.
Performance is out of this world! Verticle climp will end only due to dead battery.
The bru$shle$$ option was hard to swallow financially, but it sure resolved the performace issues, with no more weight gain than the canned 400.
I'm am changing my rudder right now, due to the full throttle flutter (plane looks like a fast moving crankbait. Flew the last couple of flight with the rudder pinned and linkage disconnected.