These Temples tend to be on bluffs live Phra Viharn in Thai territory overlooking Cambodia below .The border was established on the bluffs for military reasons ...so the Thais could overlook Cambodia below.
The border dispute over Phra viharn is facile, yes it was built by Kymers 1000 years ago but it at the top of the bluff so its clearly in Thailand , except on the old French maps and thats why there is a dispute.It would be easy for sensible people to share the access however.