It is not just the water hardness. Dirt dust on the leaves can bind to gly making it ineffective. AMS also lowers the ph of the mix making it easier to penetrate the waxy coating on some plants. AMS contains both Nitrogen and sulfur which also benefit the plot. I normally dissolve 2 cups of granular AMS into a 20 gallons water, then add gly. Depending on the AMS, sometimes I'll dissolve it into a bucket of water first, then filter it into the tank. Published mix is up to 17 lbs of AMS per 100 gallons water.
Granular AMS can clog your sprayer if you pour it in too fast. Pour it in slowly, and stir with a long broom handle or run the tank agitator while pouring. I usually use 48 oz. per 25 gallons of water.