Yep. I had the same problem. With the stock booms it's not possible to mount a battery longer than 170mm or so and still be balanced. For me, with a gimbal on the front, mine wouldn't balance without drilling out the slots on the battery plate and mounting it sideways as far back as possible.
I am going to be using longer arms (325mm cf from
rcexplorer) to hopefully go back to the stock placement.
FT should probably update the kit with longer arms because as it is, very common 4-5000mAh batteries do not fit, and many common gimbals cannot balance even with everything adjusted to the extremes.