I didn't plan on getting more than 30k out of it. You trying to put words into my mouth?
The problem with your theory is that if he runs 8 days between regens, the iron will coat the resin and won't rinse enough. He then has to back down on the number of days between regen. Now he has a bigger unit but only using a portion of it.
My theory, "won't rinse enough.... only using a portion of it". LOL
I've been successfully treating up to 5 ppm of iron like this for 23 years now.
Proving like I've told you before, you don't know what you don't know. And won't listen to anything but what you think you know. So do it anyway you want to and I'll do it the way I do it. The difference is in our customers' water, salt and water efficiencies. And you can go to the Customer comments page on my forum and see what they say, We can't see what your customer says about your way though.
Anyway, your 32k requires 15 lbs of salt per regeneration and will only get 30K actually. That is a fact proven by any resin manufacturers' spec sheet on the resin you use.
15 lbs and 30K gets your customer into a poor salt efficiency of 30,000/15 = a salt efficiency of 2000 grain/lb. And you put him into a regeneration based on 30,000, so the gallons would be 30000/120= 4680 per day so 30000-4680=25320 after the 24 hour reserve is taken out (you may do the 24 hr reserve differently) and 25320/4680 = 5.4, or a regeneration every 5 days @ 15 Lbs.
Mine he gets a regeneration on average every 8 days with 12 lbs. and there are 46 8 day periods in a year, and 365/5 days = 73 5 day periods your way. So 73-46 = 27 more regenerations a year your way times 15 lbs = 405 lbs more salt/yr, your way; plus any cost for the extra water use if he is on city water, and maybe higher sewage rates if charged based on his water bill.
With mine he uses a resin cleaner about once every 4 to 6 weeks that costs about $15.yr. 405 lbs/40 lb bags = 10 extra bags at say $5 each equals $50 more/yr - my $15 = $35/yr more your way. And he'll probably have to use a resin cleaner anyway.