Spectral filtering in passively mode-locked all-normal dispersion Yb-fiber lasers offers the great potential of realizing cost-effective, compact, alignment free and low-noise all-fiber based systems. Besides the filter bandwidth the length of the passive fiber sections before and behind the gain fiber plays a major role in pulse formation and the corresponding pulsing dynamics. In this contribution we report on experimental and numerical results on the systematic variation of fiber lengths of the different segments in order to optimize the laser system.