You want to set the idle screws evenly side to side.
you want to open till max idle rpm is achieved in gear, then readjust the idle speed screw to the desired rpm in gear.
this is sounding like a canidate for tailored advance curve.
If you could raise the initial to as much as it will still start with 'fully warmed up', you could then CLOSE the throttle plate some and get a more IDEAL alignment of the transfer slot, THIS will allow a much BETTER tune of the 'IDLE QUALITY'.
What's involved is LIMITING the amount of MECHANICAL ADVANCE.=welding the advance plate slots up some
If you could tell us more about the distributor and wether you have some welding skill.