Sometimes they are designed that way. Some people prefer a consistent look along the wall so the cover, and sometimes the pipe too, run the whole wall. If the room is near the beginning of the loop, or the heat demand is low, you can find few fins.

Why is that room cold? It is probably not as bizarre as you think. Maybe someone miscalculated. Maybe some modifications were made to the house that made the other rooms relatively warmer. That might happen because a window was added to the cold room or maybe the insulation was degraded there or added elsewhere.

I don't think that you can find fins to add. You might make some yourself, but you'd have to design them for good heat transfer (good contact) from the pipe.

Is there any way to better insulate or air-seal the room? That will cost you less in the long run. Check the attic insulation above that room to see if there is some defect and think about adding some even if there is not a defect. Take a good look at the windows and see if there is room for improvement.

Thanks for the info. The room in question is a corner bedroom on the northeast side of the house. One window on the north side and one on the east. So yes, that room by design will be colder than the others on orientation alone. I would say about 20% of the pipe in that room has heat coils on it while the bedroom directly opposite it on the southeast corner has coils the entire length. If logic had been used, it would make sense to more heavily heat the north room over the south.

Both bedrooms are directly over the unheated garage. I have sealed every leak I can find in the garage and the ceiling is well insulated. And again, the cold garage does not affect the back bedroom, so I doubt it is a factor with the front bedroom.

I had the whole house energy audit last year, and they said I did a very nice job sealing up the house. I wonder if I could just buy a stand alone baseboard, cut the coil out and wrap it around the pipe in that room?