Gradually reduce PH in Flowering? Help!

I was just reading in a cannabis horticulture book that it is wise to gradually reduce PH from 6.5 in the first week of flowering, down to 5.8 by the 5th week flowering. Has anyone had experience with this? What is the ideal PH in flowering? Thanks!

i have a guess as to their reasoning being certain nutrients being taken up better at different ph levels and flowering plants use more of certain nutrients. I've never tried it but im skeptical, what proof did they offer showing it was beneficial and worth doing?