I did the complex calculations and it comes out to 202.75 square inches and 216 square inches = 20 points. However, These have a lot of surface area being thin and small compared to something like a simple 6x6x6 cube. Therefore I am more than happy with your 30 point estimate, as I find terrain highly subjective anyway. Sure the size matters (PHRASING!) but its also about what the model is and how much detail is there.
This is a great little(ish) piece and you gave it a great paint job. Awesome work Noel, keep it coming!