Have you played around with the parameters:

pX_setsteprate(60,8,NX_TIMESTEP_FIXED);
pX_setunit(1/40);
ph_fps_max_lock=100;
ph_check_distance=2;
pX_setccd(1);

and have you used pXent_setccdskeleton(ent,vector(0,0,0),1);