Consider both the heat source and the bed's intended use before choosing that location. Bedding should not touch or obstruct a radiator unless the product is specifically designed and installed for that purpose. A warm nearby position may appeal to a cat, but it must remain easy to leave and should not expose the bed to temperatures or conditions outside its care guidance. Check the location while the heating is on rather than judging it when everything is cold. Keep fabric away from controls, pipes and other parts that could cause problems. A radiator-mounted bed needs its own compatibility and capacity checks; it is not interchangeable with a floor cushion placed on improvised supports. Provide another resting option so warmth remains a choice. If the cat's heat-seeking changes markedly alongside other unusual behaviour, discuss that change with a vet.
A radiator bed is a separate product category, not a floor bed hung from the radiator. Compare the radiator type, brackets and stated capacity before choosing a mounted design.
For product comparisons alongside this advice, see Velvet Nest and Silver Velvet Nest. The details below explain their sizes and uses.
Velvet Nest
Silver Velvet Nest
AeroMat Chill Pad