I also have some randefalk pieces. The end of the leadpipe rattles against the shank of the piece when seated fully on my besson. The gap is not the problem, as the inserted length of the randefalk is less than the inserted depth of a wick.
It feels like there’s a weird manufacturing thing with the randefalk, but Patrik says it’s not. I had Karl hammond turn the shank of one ever so slightly, and it now fits.
I assume this is also why the randefalk response feels weird to me on my besson.