Is there a height requirement in order to consider something a "ligature risk" ?

Any examples are for illustrative purposes only.

There is no height requirement for a ligature risk. Information from various sources notes that death by suicide as a result of asphyxiation can occur at any height. Specifically, there have been reports of death by suicide or suicide attempts during which patients fixed a cord, rope, or other material to a low pipe and around their neck and then spun their body ("alligator roll") to twist until it asphyxiated them. Thus, low-to-the-ground exposed piping (such as piping near toilets or under the sink, for example) or any other apparatus protruding from the wall or another structure is considered a ligature risk if the patient is able to create a sustainable point of attachment with another material in order to inflict self-harm or cause loss of life.

Additional Resource
Suicide Prevention Portal