I believe both the wet and dry screen heights were 35 feet until well after the airline fleet was mostly jets. Like 1970s or early 1980s as I recall. The justification for reducing the screen height to 15 feet for wet runways was to lower the decision speed, so in the unlikely event of an engine failure during takeoff roll the odds of being able to continue the takeoff increased, which would normally be safer than trying to stop on a contaminated runway.