fix wall/srd and fix srd

I think i cloud not represent my intention correctly.
I want to use fix srd command to treat a group of partilces as stochastic rotation dynamics (SRD) particles that serve as a background solvent when interacting with big particles (polymer) in groupbig-ID.In order to take into account hydrodynamics effects on dynamics of polymer and i need to create an impenetrable membrane towards srd particles. Is it correct to use fix wall/srd command for creating this memberane in the middle of simulation box?
I want srd paticles can do interact with both monomers of polymer as big paticles and membrane as wall/srd.

This is the Q I answered previously. I've never used
fix wall/srd in the middle of a box, but you can try
it and see if it does what you want.