Been using the AFT tank first for a long time now, after AUX tank when (usually) in A series. Staga, The AFT fuel tank is behind the Pilots seat, forward part of the AFT tank reaches the back part of teh pilots seat. The FWD fuel tanks back part start right under the pilots seat and contineus forward a bit.
COG in the 190 is "about" where the wings go into the plane, slightly behind the middle of the wings. The AFT fuel tank is stationed behind the COG and, carries (in the A5) 50% of the fuel.