Settings for Aroma vs Whirlpool hops

[J A]

I can't find much info on the "Aroma" option in the hop section. It reacts similarly to Whirlpool but where the Whirlpool option only calculates based on utilization percentage (not time or temperature settings) the Aroma IBU contribution reacts to both utilization percentage and time (but not temperature).
What's really being tracked by the Aroma addition?
I try to figure IBU contribution from hops added at flame-out and left through chilling. That's usually 15-20 minutes from 212 to 90 or so. The amount of time spent at temps important for hop uptake is minimal but the 5 minutes or so above 170 will account for some IBUs.
Anybody use the Aroma setting?
How are you calculating flame out hops and how long do you leave them in?

 

[Ozarks Mountain Brewery]

I'm not sure what's being done now but in the past those were all just titles added to the recipe and no formula was added by selecting them, that may change though

 

[HighVoltageMan!]

Most of the whirlpool/flameout hops would be really hard to calculate. I have just played with the numbers until I got what was a fairly accurate number, basically I went by the seat of my pants.

I'm starting to believe that IBU calculations are basically an educated guesses. The type of hop, pH of the finished beer and the type of yeast all contribute to or take away from the overall bitterness of the beer. I guess for flame out hops, I would start out at 3% of utilization and go from there.

 

[J A]

I guess for flame out hops, I would start out at 3% of utilization and go from there.

That's in the ballpark of what I've started using. I find based on some taste testing that Whirlpool starting at 180 and turning off the chiller coil flow for 20 minutes puts me in a 4% range. The flameout hops starting at 212, dropping in temp but staying in through the most of the chilling process should give me that much or maybe a little more. In fact if I assume that there's a minute or 2 that the temp is high enough to isomerize at close to the rate when it's boiling, I'd probably see something like 10 percent.
BTW, Ozark, switching between the Aroma and Boil setting doesn't change the IBU contribution, so the formula it's using is the same.