The K of capacity of all softeners is adjustable.
Softeners are sized by the cu ft of resin in the tank, that cu ft dictates the size of the tank used and the salt dose in lbs dictates the K of capacity per regeneration.
The 32, 48, 64, etc. etc. is basically inaccurate because you regenerate 1.0 cu ft to the maximum K of capacity (30K) with 15 lbs. So a 2.0 is a max of 60K @ 30 lbs. 60,000/30 = a salt efficiency of 2000 grains per lb. @ 6lbs/cuft = 12lbs you get 40K, or an efficiency of 3333 grains per lb. which is much better salt efficiency. You say you need 27K, and in a 1.0' you would need 14.5 lbs for 27K, in a 2.0 only 8 lbs. That's 6 lbs saved every 8 days or so.
A 2.0 has a constant SFR of 13 gpm. A 1.0 has 9 gpm and a 1.5 has 12 gpm. Exceed that flow rate and the softener can not remove all the hardness.
You should use 75 gals/person/day instead of 60.