If you don't know what Atkinson VCT timing is or why having ignition happen before TDC increases power this may not make alot of sense.

While the engine is in Atkinson timing there will be less Fuel and Air in the cyclinder as well as less compression pressure due to the length of true compression time.

Having the ignition ignite the charge soon takes advantage of the expansion of the explosion time while the cylinder volume is being reduced. This builds more peak pressure and gives a more complete burn. The less fuel/ air the weaker the explosion so igniting it sooner allows for more expansion and more peak pressure. As throttle is open and more fuel and air is put into the cyclinder so the explosion will be stronger ignition must be closer to TDC or even ATDC when RPMs are low and Rotating assembly inertia/ piston Max speed is low. As rotating inertia and Piston top speed increases ignition can happen sooner with out countering a significant amount of inertia, but increasing cylinder pressure and power. Balancing all these events creates the highest peak cylinder pressure for optimal performance. its also important to a well running engine.

Understanding this shows why FI ingintion can not be as far before TDC as N/A due to the amount of fuel and air actually getting into the cylinder being far greater.

Higher cyclinder pressure means Higher torque. Higher explosion strength means more HP.