Efflux coefficient fluent
 

I'm simulating a convergent divergent nozze in fluent. My porpouse is to reach the geometry wich gives the major absolute pressure at outlet, and i thought that it would have olso the minor pressure drops couse pressure inlet is fixed. But I noticed that decreasing the inlet diameter decreases the inlet pressure, and so the pressure drops, but the pressure at outlet is minor then major diameter. So if i consider pressure drop the best convergent i should take is with costant diameter so not convergent, but this should have problem with efflux coefficient in inlet, so how can I set efflux coefficient in fluent?