  For small samples, the modification of the XRR profile by the geometrical
factors manifesting due to profile and size of the beam and the size of the
sample is significant. Geometrical factors extend till spill over angle which
is often greater than critical angle for small samples. To separate the
geometrical factor, it is necessary to know the spill over angle. Since
geometrical factor is a smoothly varying function and extends beyond critical
angle, it is impossible to determine the spill over angle from XRR profile of
small samples. We have shown by comparing the normal XRR profile of a small
sample with the XRR profile taken with a surface contact knife edge on the same
sample, that the spill over angle can be determined. Thus we have developed a
procedure for data reduction for small samples and validated it with suitable
experiments. Unlike hitherto used methods which have drawbacks, this is a self
consistent method for data reduction
