What is the minimum distance you must leave clear when parking outside a built-up area before a St. Andrew's Cross?

You are correct. When parking outside a built-up area (außerorts), you must leave at least 50 meters clear before a St. Andrew's Cross, which signals an upcoming railway crossing. This rule ensures that vehicles do not block the view of the crossing or obstruct the path for others, so everyone approaching the railway crossing has a clear line of sight and enough space to stop safely. Inside built-up areas, the minimum distance is only 5 meters, but outside it increases to 50 meters for greater safety due to higher speeds and reduced visibility. Remember this distinction for similar questions.