Struggling to find radiators this size. Would like oval tube type ideally but anything that heats properly would be a start. Any suggestions please. To replace two 'ecorad' 600x2600mm (HxL), neither heat well - cool in the middle (hot top and bottom) even when only radiator on and pump on max. System also has Kudox radiators which heat OK and some oval tube verticals which also heat well. Many thanks!