You are correct PaulieWaulie about the plant being in charge.
Meaning they decide what they want to uptake by what exudes it sends to the roots.
Myself i prefer my medium to be light in amendments (mix in globally) and leave what i call buried treasures featuring P & K on the bottom of my flowering pots.
My vegetative pots are done this same way only it features higher N.
I think one of the important things to remember is that mychorrizal fungi is responsible for much of the uptake of phosphorus.
Do you know that liquid P only retards the growth of the fungi, so no liquids !
Also fertilizer with high ratio of P also retards this growth.
I try and not use any fertilizer that has a higher ratio of P then a 8 during flowering.
Being that P and K are the elements most needed for flowering but I do not change my vegetative elements until after the stretch is over ,approximately 2.5-3 weeks after clock is set back for the plants still need much N to build the mass that is needed for bud development.
I'll do this with top dressing of N my favorite is 10-2-1 bat guano, I mix it with some worm castings, the guano's are readily available for 10-12 days.
When I make teas i do it for the beastie's that they bring not so much a feeding.
A good care taker provides what the plant wants at the right time but always give the plant the choice if it wants to uptake it or not.
By leaving a table spoon or 3-4 of P & K here or there on the bottom of your containers instead of mix in globally is the key factor.
Hoping for you to reach that next level!