After much time i finally figured out how the reference desing uses such tiny trace width for the ddr routing . They had to use such small trace width to route it between the bga pins but that would not be the needet 80-100ohm impedance on the noncopular differential pair . The trick was they used a different trace spacing to archive around 120ohm +- toleranze ! I also have redone some of the bottom caps for easy routing and no interferance problems !