It is true that the manner in which radiator valves are installed can factor into altering the Delta T value of hot water radiators, considering that the ratings are born of the connection between radiator water temperature and that of the ambient room temperature delivered by the central heating system.
Essentially, to ensure that best practice is followed in producing the full BTU output, lining up with the accredited Delta T rating, is to fit the flow valve at the top of the radiator and the return valve at the bottom, at the opposite side to the flow.
To find out more about Delta T values and their importance to your home heating choices, browse our blog, Understanding your heating output – A guide to Delta T radiator specs.