My light hearted observation was prompted by an assumption that since there is no (significant) net heat gain, one fluid body loses as much heat as the other gains, and a second assumption that it would work as well whichever was the hot side, and whichever was the cold. Add the (uninformed) gut feeling that the tubes were more vulnerable than the shroud to blockage, and I'm there.
To get best exposure to the Fuel (which isn't so cold when low,) the design (IMO) slows the Fuel down, by necking down the cross section and adding surface area F/O.
But reflecting on your post, the contact times for a plug of each fluid are not necessarily the same, so maybe the symmetry is broken...
the need for an FOHE is debatable, especially when Thrust is way short of TOGA or Cl. Hence, why not a (relatively) simple bypass for the Fuel?
There is no difference between us in the logical need for a bypass mechanism. I just liked the idea of a (very) simple one that does not rely on a moving part, and which puts any ice right in the heat exchange zone. Can I have it as well, please, just in case the (relatively) simple one with a moving part gets wedged open by a lump of the ice solid in below zero fuel when TOGA is needed. That scenario would be the very devil to diagnose from the expensive later consequences.