  In November 2010, the azimuthally symmetric WASA detector and the polarized
proton beam of COSY, have been used to collect a high statistics sample of
$\vec{p}p \rightarrow pp\eta$ reactions in order to determine the analyzing
power as a function of the invariant mass spectra of the two particle
subsystems. Here, we show studies of the influence of the beam and target
characteristics such as location and direction on the determination of the
polarization.
