That's good to hear. Right when my JH13 arrived, I wondered why anyone would want more bass than the 13 had... it was quite bountiful.. maybe even bordering on too much for my tastes.
After the aforementioned use w/ the JH13, whereby the bass tightened and flattened, I began to see how a little more bass might be in order for the bassists and drummers (and, perhaps, the "traditional" bassheads). I do listen to a lot of hip hop, electronica, drum & bass, etc., but I'm not a basshead in the "stereotypical" sense: a "more bass is never enough"-type of listener. I prefer a linear, low end response.. that must be very technically adept. I am ok w/ it if if it's gently boosted.. as long as the lift is wide and even .. not mid-bass centered).. and not to the point it dominates the acoustic signature. Given these preferences, I found the JH13's bass to, quite simply, be perfect. It's got an eerie ability to sound absolutely subwoofer-like (when the recording demands it).. the midbass is, again, just perfect in that it provides a sense of articulate warmth w/o ever creeping into the midrange.. but the low end maintains blistering speed, clarity, and an effortless ability in the way it textures.
My ears are a bit spoiled in that the two phones I alternate between on a daily basis are the HD800 & JH13. Presentation & tuning differences aside, for me to not feel any kind of a significant drop off in technical ability speaks volumes about just how special the JH13 is. So much so that I actually sold the HD800. There was a practical side to that decision (I needed to go to a more portable rig), but it also indicates how impressed (and content) I am with the JH13 FP.
I'll also echo shotgunshane's sentiments in that I find the JH13 FP's tuning to sound very much along the lines of the "Olive-Welti curve."