All Mule headstocks are slotted these days. I don’t know much about classical guitars but there’s some misconception carried over from them when it comes to stringing up your steel string Resonator guitar . There’s no need for any loop-dee-loos or tuck unders here.
Stick the string all the way through the hole. Give it three fingers width of slack and push it back through. Wind it to the inside of the post.