The forward scatter relation with size only holds for very small
angles. This depends on the exact cytometer configutration (e.g. the
kind of flowcell you use). The small angle forward scatter is related
to diffraction, which is proportional to the cel/bead size.
The best thing to do if you are using a FACScan or likewise apparatus
is to tape off the outer side of the forward scatter detector. Only scatter
light around 2-5 dgrs. will be measured in that way.
These angles are within the diffraction lobe of the forward scatter pattern.
You can do a bead experiment to see if the amount of taped off
detector area is enough. As the highest intensity is in the small
angles, no problems regarding signal intensity will occur.
Good luck.
Robbert van Leeuwen
Applied Optics / Flow cytometry Group
University of Twente
The Netherlands.