Whats the best position to mount Hydor heaters? Can I use the Heater for Terrarium?

Hydor theo heaters need to be mounted close to water flow from a pump using the suckers provided ( due to the Hydor heaters low operating temperature the suckers can be mounted on the element itself ) Hydor recommend that the heater is mounted in a slight diagonal position to allow the heater to spread heat more easily. The heater can be positioned horizontally  for terrarium use if required.