Yes. But it's not really the ionic content that affects attenuation. It is the mash pH that affects attenuation. Low pH tends to enhance fermentability and high pH tends to reduce it. Of course, this only applies within the typical mashing pH range of about 5 to 5.8. Outside that range, there can be other factors. Be aware that the temperature and duration of the rests also have a substantial effect on attenuation capability.