In article , Colin
Stamp writes

No. I would expect convection to be the driving force in deciding which
channels the water flows through. If hot water finds itself at the
bottom of a cooler channel, it'll flow strongly up it. With the exit at
the top, a large pool of cold water will accumulate at the bottom of the
rad.

I've seen this very effect on a system I was balancing for a pal. All
rads TBOE but one wouldn't balance correctly and room temp was down.
Large pool of cool water from the bottom up was exactly how is
manifested and swapping the flow solved it immediately.

Also, whacking more flow through makes little difference, you get a
little more mixing but half the rad is still cold so I wouldn't expect
more than half output from it and that would be geometry dependent.
--
fred
it's a ba-na-na . . . .