The K of capacity of every softener in the world is adjustable... note his manual talks about adjusting the salt dose? Why would they do that if my comment was false? You adjust it by using more or less salt. Any "30K" (meaning it has 1.0 cuft of resin) softener is using 15 lbs of salt/regeneration or it is not getting 30K.
To find the salt efficiency, you do the same as figuring fuel mileage; 30,000/15lbs = a salt efficiency of 2000 grains per lb.
Setting the salt dose lower, say to 6 lbs gets 20K (you find those figures on resin resin manufacturers' spec sheets for the resin being used. And 20,000/6 = a salt efficiency of 3333 grains/lb. So the volume of resin should be sufficient to provide the higher salt efficiency to cover the K of capacity needed for a regeneration of once every 7-8 days.
And then there is the constant SFR size of the softener, which is dictated only by the volume of resin in the tank. The constant SFR (gpm) must be higher than the peak demand flow rate (gpm) of the house.
The constant SFR is what is used to size all softeners or filters; sad to say, most dealers do not do that, they talk "30K" or "45K" etc. but never get into SFR or how to figure the most efficient salt use for the softener. And IMO far too many are like used car salesmen.
The reason Culligan says to adjust the float is because the float when raised by the 'extra' brine water shuts off flow preventing anymore water to flow into the salt tank. That is to prevent water overflow onto the floor or they are using the float to set the salt dose (3lbs/gallon of brine refill water).