I was looking into obexd at the time I came across this issue. And I do not remember how I measured the size exactly, but my use case was copy files from the phone to the PC via obexd. I then tried the same with the old N9 and it was mind blowing 32K. So how could it be that the older N9 hardware had higher output rate?
I am starting to think that it is either configuration as you suggested or some bug somewhere that affects more modern devices for some reason.