I'm troubled by the notion that all ILS approaches universally arrive over flat terrain. I'm not sure of the relative details of places like Bristol and Leeds or especially places like Sao Paulo Congonhas but they certainly would appear to be problematic when it comes to Rad Ht at DA.
Troubled by what? Rad alt height at DA is a complete irrelevance! If you fly a Cat 1 ILS in your Trinidad Tobago (small SE aeroplane....), you will have no idea what the rad alt height is, and have no need to!