The 80/20 or a higher mix will over correct and you won't like the water then. Plus it eats up the 'corrosex' quickly which then prevents you getting to 7.0 eventually.
You should have like a 2.0 cuft unit; assuming the pump could backwash it successfully. There is a SFR (service flow rating) for all filters and softeners, your 1 cuft AN filter's SFR is probably like 3-4 gpm meaning, every time you run more than that gpm through it, it can't adjust the pH that fast/quick and it won't be able to get to 7.0, and maybe only 6.2 etc..
Yes if you are going to buffer acidity, you want neutral pH of 7.0 although the guvment says you're OK with 6.5 but they used to say below 6.9 wasn't good enough.