you should add quilting in the sashing strips- 2"-4" does mean in all directions- batting that does not have 'scrim' tend to need to be quilted this closely- what happens is- when the quilt is laundered the areas that do not have enough quilting to keep the batting stable will pull apart- and bunch up- so you will have empty spaces and then globs of batting balled up inside the 'channels' so if you add at least a line across the strips every 3-4" you should be fine- but leaving long unquilted channels 'could' with wear, time & laundering cause problems. when a batting says you can have up to 10" apart- it has a scrim which keeps the batting more stable with time-