I think it is time to completely eradicate the low P thinking. Many of us now are finding the higher levels of P, 2-4ppm, don;t cause problems and actually help many plants frow better. It seems to cause more vertical growth and brighter, more intense green colors of plants. What do you give terrestrial plants when you want them to grow strong and bloom? P. It is starting to seem to me, from my very limited experiences and from much reading and assuming from other people's experiences, that there is only one reason to limit P, to slow the plants uptake of N and thus limit growth in general, making tank maintenance easier. P does not cause algae, and actually increasing P usually helps to eliminate spot algae in high light situations.
So, it guess its seems that to bring out the reds, you would keep PO4 the same but lower NO3 levels. This would be a lower ratio correct. Say you switch from 10:2 N

(that is a ratio of 8) to 6N:2P (a ratio of 3) That should cause plants like Rotala indica, etc. to produce much redder coloration. this example assume obviously that all other factors, CO2, Trace nutrients, etc, are of appropriate levels.
14.5:1 ratio I do not think is necessary. Plants survive in nature with much less and do fine. They may not look like our tanks buthey certainly survive ad propagate themselves. I think that the levels need to sustain life ar very low, it is the growth that we often strive for in our tanks that are much higher. Maybe someone else could shed more light on this part.
I feel like much of the ratio discussion, exactly how much do you use as opposed to me, is more geared to someone new, or to a new tank. I think it is a way to easily figure out a "safe" range of nutrient levels to get best growth quickly without becoming toxic, making sure no element is limited and basically giving your plants every opportunity for survival, thus limiting algae growth and getting you tank off on the right foot. This is certainly not to say the ratios and nutrient levels are not important to the experienced aquatic gardener, I think they are the ones who figure out the most and help the rest of us.
Will 3:1 ratio grow plants? Will a 20:1 ratio grow plants (obviously, as long as nothing else is limited)? I think the answer to both is yes. I think the questions are really, which is easier to maintain, which suits the individual aquarist best, and their plant species, tank conditions. lighting levels, etc. It seems like anyone can grow plants as long as they give them enough or more of everything, its finding the "sweetspot" that gives optimum growth and expected, desired results that we each are searching for. There are a lot more closet mad scientists out there than are admitted I think

I know I am one of them
Together we can help each other find what works best for us, even though someone else may find something different.
And now I am rambling.