Dear,
If I understand well the point...you want to assign a fixed bin to a certain material.
Please note that you need to open the material master data WM2 view at storage type level....and then you indicate the fixed bin. See images below:
in your serrching strategy for the storage type, you have to point to the storage type with the fixed bin strategy, then the system will check which bin the material is assigned to
Hope this is helpful
BR
Claudio