Center of gravity for a CNC machine

I guess that the center of gravity for any CNC machine should be as low as possible. But, how low? Lets take as reference the upper surface of the machine table. What if the center of gravity is above this face?.
Thanks in advance!
Best regards
Felix Pico

Run a natural frequency analysis on your structure and you'll find out right away e.g. model an enforced displacement of the table; linear XC, velocity 200mm/s; hope you like disco and dancing ;)