Some manufacturers state that flares can add up to 3db higher output by raising the point of where port noise is audible. That can be simulated in the program by cutting the max wattage in half.
The sims are usually show an allowable limit and your limit for port airspeed. I find them to be worst case scenario. Mostly cause the airspeed usaully only goes too high at max output. If your like me I very rarely play my HT/music that high. Also, It won't really chuff on anything but program material that is around tuning(abou22hz-16hz) so do to lack of material most of the time you'll never reach that point unless your playing something sustained like sinewaves at tuning.
Port airspeed would probably be more of a concern in car audio aplications where the tuning point is much higher and smack in the bandwidth of most music material. But do to high spl most people listen to in the car, inaudible