A quarter turn to a standard die produces some 18 thousants of change; that's a huge difference when making bottle neck case headspace adjustments!yes, just back off the full length die to achieve neck sizing only. It doesn't take much backing-off, I usually back off 1/4 of a turn.
There is no reason to adjust bottle neck shoulder set back for one or two thousants, fired case's lengths spring back that much same as does case diameter.
IF we want max case life as well as easy chambering simply adjust the FL sizer to duplicate the fired shoulder length, there's no need for sizing it back any further.