If the condition \(\mu l < 1\) is not realized by the investigated samples, we use \[P= P_0 + C \frac{\tau}{sin(\theta)}(1-\frac{\tau}{sin(\theta)})\] where \(\tau\) is the normalized surface roughness parameter, \(P_0\) is called the bulk contribution to the microabsorption effect since it depends only on the parameters \(\mu\), l and \(a_0\) which characterize the structure of the bulk materia. The explicit representation of P0 and C as function of the bulk parameters a0, \(\mu\), is only reliable in the above conditon. However,  the algoritm could be nevertheless applied as the simple analytical form of the \(\tau\) and \(\theta\) dependence of the microabsorption correction factor is however retained.
It is exact if \[\tau^2 /sin(\theta) << 1\]  The surface roughness parameter of real powders can be expected to satisfy the condition \(\tau\)<0.3. (The present analysis yields 0.005 <1-<0.12 for the investigated powders.) Consequently, expression can be used without any restriction in the range of scattering angle \(\theta\) > 30" (for \(\tau\)=0.1: \(\theta\) > 10°). If it will be necessary to record scattering data of rough samples at scattering angles \(\theta\) < 30 the surface roughness parameter \(\tau\) should be fitted. Then, the value of \(\tau\) should be used to estimate the range \(sin(\theta) > \tau \) where expression is applicable.
some values for a not pressed powder (BSCCO) P0=0.6 C=1-2 \(\tau\) = 0.005-0.1