Seed shells being tough from phosphorus or potassium during seed run

[Moatsy]

Howdy all. Once upon a time I came across an article that mentioned that when doing a seed run, you don’t want to feed your pollinated mother high amount of Phosphorus or maybe it was potassium as this results in a harder, thicker shell on your seeds. They suggested giving a slight nitrogen boost during flower for the better development of the seed embryos.

I, for the life of me, cannot find that article or information again. I was wondering if anyone had any scientific information about this or even just some experience of their own they could share?