Simple answer: it doesn't need to.
The ATTITUDE of the aircraft (bank, heading, pitch) can be measured anywhere on the aircraft, because it is constant throughout the aircraft, unless the aircraft is made of putty.
So if the gyros sense a 5 degree shift in pitch, the whole aircraft has (to any reasonable approximation) moved 5 degrees in pitch. As long as the sensors are firmly fixed to the structuire, it won't matter where they are.
now, sensing accelerations is a different issue. Those WILL vary with location in the aircraft relative to the cg. Any accelerometers will be put as close to the nominal cg as they can be; things like FDR accelerometers are located specifically.
If anyone ever needs to correct to the true cg accelerations, you'll use the sensed angular rates to strip out the terms due to the offset sensing 9from a known or calculated cg position) but that's more an analysis task than a task for the AHRS.