The idea of a common screen height seems eminently sensible and difficult to defend the difference. Safety is safety, and if missing the hotel by 15' is OK on a rainy day, why not also on a sunny day? On some runways it is possible to have a higher weight on a wet runway than dry, but some operators don't allow you to do that: you have to check both and take the lower. 35' is safer than 15', perhaps, but on some days 15' is considered not to be. It is or it isn't? Go figure. How to make an easy job difficult. I wonder if any of the muppets at mission control have ever bothered to think about it. Indeed, would they all even understand the question? Sorry; I forgot my anti-cynic pills today.