In reply to Oujmik:
It might be that was where it was easiest to pull the pipes up.
It might be there was some furniture in the way of a bigger unit.
It might be well insulated meaning a small rad' is adequate.
It might have been cost cutting or from a cheap job lot.
The installer may have been a fool.
They may have prioritized heating other rooms with bigger rads in the days before thermostatic valves.
jk