I just re-built my largest 12″ quad, the “bumblebee” with the fireBLDC 1.2 brushless controllers mounted directly under the motors under round aluminum carrier plates. This is really the way these brushless controllers are meant to be installed:
Of course the cable routing could be better (inside the riggers and through the aluminum plate), but for testing/quick installation, this is ideal. The first two flights were excellent, the quad really makes a nice humming sound when rising at full throttle, like a church organ pipe ;-). The CAN bus makes it extremely robust, so no fears of I2C bus errors here, even with long cabling. I also put some position light LEDs at each end, because the fireBLDC supports to switch one LED for this reason. Sadly I decided to use only a microcontroller GPIO, so the LEDs are very dark due to the little current. For the next version, I will use more powerful LED drivers.