I'd say you should experiment with Slic3r
it can manage extrusion in very sophisticated way
it can overextrude if you need a line wider than actual nozzle size as same as it can underextrude if needed it can even change extrusion continuously while extruding one line
i use mattercontrol
take a look here - this is the same object the same layer and slic3r as slicing enginethe same settings
please notice - this object has wall thicknes exactly 2 times nozzle diam
here is what i get with