What you have been noticing is commonly referred to as BRS, what you may not have noticed yet is that the roots are shorter.
It is important to remember that there is no "Magic Pill" or as in this case no "Magic Powder".
Although "Magic Pixie Dust" appears to be real.
'Pixie Dust' made from pig bladders regrows limbs of wounded soldiers | Mail Online
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Indeed many manufacturers of mycorrhizal inoculants add other ingredients to increase product efficacy.