heya jack congrats on being half way through yer biggest yield ;-) I'd say dusto is right the more plant ya have the more they are gonna have to eat so just put @ MAX 100ppm (almost all P if you can) if you do it in the morning you should definately notice burn signs by shutoff and if yer in close tune with the plants you could probably see the signs of nute burn before the tips curl and yellow/brown take a couple pictures to help compare

Once you notice too much food especially if it's curled tips or yellow/brown edges I'd top off 2 days with just water and see what the ppm is cause the plants will dump out there excess and that should be a good indication of how much they want

I'd say you definately want to make sure they have enough at all costs but being slightly under the max intake is probably ideal it's also possible the potency/taste/smell might be affected by doing this as well so just try to keep records of what ya do and if you liked or didn't like the change

Do you think they may be able to get a 1/4 lb from one plant this time?