http://delhidefencereview.com/2019/04/03/all-you-need-to-know-about-the-pdv-mk-ii-indias-satellite-killer/
In the above article by indranil , he wonders about the purpose of the 8 vents/ports at the base of the PDV stage ( 1st stage ), just above the 2nd stage interstage.
AFAIK those 8 ports...