No idea if that trick works with the F5.2's and frankly I'm not buying another set because they disappointed in other areas as well (in terms of sound and looks).Nothing that some polyfill in the speaker would not take care of. I got +6db boost with polyfill and had to reduce the amount of polyfill to keep it a bit more balanced.
You should message some of the reviewers that have the F6.2 and tell them about the polyfill experiment. I'd like to see some comparison graphs between the before/after.