buffer

hi,
I am trying to do spin transport calculation using siesta 4.1b3.
Electrode and scattering region atoms are different in my sytem. So few layers of electrode atoms are included in the scattering region.
When I calculate current through the system without specifying electrode type atoms inside the scattering region as buffer it gives current in the range of 10^-8 A. But when i mentioned them as buffer using the tag
%block TS.Atoms.Buffer
atom [ 29 -- 42, 55 -- 75 ]
%endblock
it gives current in the range of 10^-35 A.
1) How does it happen? What would be the problem?
2) What all things has to consider and tags has to given while using buffer?
3) In the parallel magnetic orientation case, is there any difference occurs in these 2 cases
  a) mentioning electrode like atoms inside the scattering region as buffer
  b)considering electrode like atoms in the scattering region also as device(ie same structure, without mentionig buffer)