One poster made an intelligent remark a few pages back about the phase shift occured by a few inches long duct relative the several meters long acoustic wavelength at that frequency. It's marginal.
A better image of what the low pass filter does is more like an additional mass, spring and damper between the driver and the ear canal. You effectively get a bandpass acoustic filter. It's been over 15 years since I looked into subwoofers so memory fades but, as I recall, the issue here isn't the phase but the transient response. In particular, You don't want to get too much overshoot at the main resonance frequency as it's been related to perceived "uncontrolled / wolly" bass.
From my short audition with the 846, it was more the quantity of bass than the texture I had an issue with while using straight from the iphone 5. It appeared all cleared using the pico power. Now that demos are getting into the stores, I will spend more time to revisit this.
For the comments from the mook festival about it being much worse than all other iems such as jh13, I am at a bit of a loss to understand it. I don't recall such experience from the tokyo show and I was rather partial to start with since I heard the 846, jh13fp, and other westone (top model ciem, can't remember the name) for the first time on that day. At least, compared to the 535, there were very substantial improvements (immediately noticeable on an A/B listen) in terms of cohesiveness and lack of compression / distortion. If it wasn't for the bass excess from the iphone. I'd own one by now I think.