Yes letting the mud build up lowers efficiency. Yes wet skimming is better for this issue. There are plenty of reefers who will skimm very very wet and use it for water changes. I have thought about this as an Idea for some time. Most of your better skimmers have a drain plug in the cup so you can have it drain into something else. so why not put fresh salt water in you ATO and a waist line on your skimmer. Turn it up and have it do a water change like that. It would take some creativity but it could be done. Maybe put a timer on your Skimmer so it doesnt use up all your ATO water and run dry but I think you get my idea