I saw that formula somewhere (on this forum maybe?) with the target ranges and thought it would be difficult for my grapes to be in the target range ( which I don't recall). The lowest PH I measured this year(with strips) was between 3.6 and 3.8 and I think the brix was 14-16 but didn't document it. With the soil I have and the heat in August, early September I just don't get the acid. Last year was my first year making wine. I don't have a ph meter and last year didn't even have strips (the local supply store had none), but they did have an acid test kit. I measured last years finished wine this summer with strips and it was 4.4 or higher. The brix of the malbec must was around 25, TA 0.42, the tempranillo was 23, TA 0.50. My wife liked the Tempranillo better, my family the Malbec. I didn't adjust the must - my current philosophy is "I get what I get". I suspect that the longer I continue the more likely I'll abandon the "I get what I get" philosophy.
I'd probably worry more about it if I planned on aging the wine. But all of last years bottles are already gone.
So far, I'm repeating all the mistakes others have made and advised against but it is useful to see the results of non-traditional approaches to appreciate why the traditional approaches are what they are.