If I remember correctly, the minimum clearway you can declare is 60m, however this is all some airport operators do declare even when the first significant obstacle is much further from the end of TORA.
Why is this I wonder; airport owner too lazy to get a survey done?
Unfortunately the operators have to use the published figures and I have known this to cause an aircraft to have to depart with a reduced fuel load then make a tech stop to pick up more fuel for the journey, rather than go non-stop.