you can treat your whirlpool like a boil in some circumstances. The longer you whirlpool, the more perceived bitterness. The hotter you whirlpool, the more perceived bitterness. Also I sound like a crazy person saying this, but my two least favorite terms right now are IPA and IBU, both don't hold a lot of meaning these days (except for IBU when brewing traditional styles ONLY, but IBUs can't really apply to NEIPA these days in my opinion.) The old research and teachings tell us things like "flameout and dry hop additions contribute no flavor, only aroma." Well wait a second, how can that be true? Adding hops is adding hops, period. Yes they react in different ways, but there is definitely SOME kind of flavor contribution from whirlpool and dry hopping, or else why would we even bother? And why would commercial breweries be switching to exclusive whirlpool and dry hop methods for their "IPAs". Sorry, ranting.
Whirlpool hotter for more bitterness, whirlpool longer for more bitterness. I can't tell you how you prefer your IPAs. I can only offer my anecdotes. I like to start cooling my wort to 170, then add all the hops and stir hard, and just continue cooling down. The time it takes to cool the wort down is the amount of time I like to have the hops in there, gives off the right flavors for me, i just need to target using the right amounts, which is typically 8-16oz per 5 gallon batch, 8oz being fairly light on hops and 16oz being fairly heavy handed. Then I place a fresh batch of dry hops in the fermenter BEFORE transferring the wort (a trick I read about from Scott Janish), then filter out the whirlpool hops, transfer into the primary on top of all my dry hops, pitch yeast, and go. No further dry hops after fermentation because I guess I'm lazy, and I like that all the hops get the biotransformation going on during fermentation. Plus the yeast and amount of time in the fermenter will clean up any grassiness. I like pure sweet fruit flavors from the hops.
