Never had an issue getting really low action on my Rics using the bridge and neck adjustment only , only time I touch the nut is when the string gauge is a bit too tight , when the nut grabs the strings, you can normally achieve low action with bridge and neck adjustment , once you start adjusting the nut, it is easy to screw it up , you can't put material back on there, look at adjusting the neck and bridge over a few days to get the action you want, get it near let the neck settle for a couple of days then, do finer adjustments let it settle and so on that way you can get exactly what you want , you need patience with Ric adjustment, hope this helps you.  Been playing Rics for over 40 years now, they are superb when you get the set up right.