If you need more sleeping of CO2 then reduce the amine solution rate. The 200 - 250 CuM/hr rate is very high amine rate.
I do not know about your gas specification and amount of gas process. Can you pass on some more data like voume of gas process, inlet amine temperature, operating pressure, tower dia., amine solution concentration ect?
Normally amine absorbtion column with 16 trays is optimum and maximum is 20 tray column.You can meet with the specification of 4PPM H2S in out gas with this.