Reflect user Velocity

[BigMac]

This is what i got so far but doesnt work all the time

new Float:origin[3], Float:oFar[3], Float:oRetNormal[3];
pev(id, pev_velocity, gsz_set_velocity[id]);
pev(id, pev_origin, origin);
oFar[0] = origin[0] + (gsz_set_velocity[id][0] * 8192.0);
oFar[1] = origin[1] + (gsz_set_velocity[id][1] * 8192.0);
oFar[2] = origin[2] + (gsz_set_velocity[id][2] * 8192.0);
fm_trace_normal(id, origin, oFar, oRetNormal);
gsz_set_velocity[id][0] = -2.0 * (gsz_set_velocity[id][0]*oRetNormal[0])*oRetNormal[0] + gsz_set_velocity[id][0];
gsz_set_velocity[id][1] = -2.0 * (gsz_set_velocity[id][1]*oRetNormal[1])*oRetNormal[1] + gsz_set_velocity[id][1];
gsz_set_velocity[id][2] = -2.0 * (gsz_set_velocity[id][2]*oRetNormal[2])*oRetNormal[2] + gsz_set_velocity[id][2];


I want it to reflect the user velocity for
Height and Forward Speed