The rate you use use should be determined by the hardness of your water.  We routinely run 17.5 lbs/100 gallons of water at 15 gallon per acre rates.  I believe Liberty calls for 3 lbs/acre and is often sprayed at a 20 gallon per acre rate.  I'd be more concerned with using the right rate for your conditions and killing the weeds than the little bit of cosmetic leaf burn it might cause.