srd fluid and lj fluid

When i created a system composed of a group of particles as fluid particles , a bead-spring chain as a polymer and a group of paticles as a frozen wall that they do interact together with lennard-jonse forces as follows:
group wall type 1
group polymer type 2
gruop fluid type 3

velocity wall set 0.0 0.0 0.0
velocity fluid create 1.0 87287 loop geom

pair_style lj/cut 2.5
pair_modify shift yes
pair_coeff 1 1 1.0 1.0 2.5
pair_coeff 1 2 1.0 1.0 1.12
pair_coeff 1 3 1.0 1.0 1.12
pair_coeff 2 2 1.0 1.0 1.12
pair_coeff 2 3 1.0 1.0 0.0
pair_coeff 3 3 0.0 1.0 0.0

fix 1 wall setforce 0.0 0.0 0.0
fix 2 polymer nve\sphere
fix 3 polymer langevin 1.0 1.0 10.0 904297
fix 4 fluid nve

Where interaction between fluid/wall particles is repulsive and fluid partiles can not move thru wall
But when i use fix srd command instead of fix 4 fluid nve in order to create implicit solvent instead of explicit solvent to reduce simulation time and i set epsilon=0.0 for all pair_coeff except pair_coeff 1 1 and 2 2 and 1 2
I observed srd particles as implicit solvent can move thru wall
Please help me how i can create interactions between srd/wall particles such as between ljfluid/wall particles?
Thanks
samira

Are both the wall and polymer particles in the same
group that you specify as "big" for the fix srd command?

Steve