Hey zem,
yeah i do agree in general, i mainly just want to experiment really, that's why mixing up your own nutrients from scratch can be so useful , from seedling to early veg for root development and just for the transition period.
currently using a store bought dry premix with micros at 4.5-1-5.5 and i'm in early veg, so as p seems a little low in the ratio i figure up it to a to a 5.5-2-5.5 / 6-2.5-5.5 and experiment with map for more vigor as p also promotes energy in plants.
i'm also using fulvic acid as a ph down, so with such a low p value there's no extra p from ph-ing, sure is a bit of added potassium with the ph up.
so your dose of ammonium nitrate is from your calcium nitrate or are you using straight ammonium nitrate salts?