The LOD for the Solstheim Mushrooms (DLC2Mushroomtree...) is abhorrent. The Vanilla LOD models match nowhere near close to the full. (done on high mesh rules)
I was able to fix it by making my own mesh rules in DynDOLOD, but for the future maybe DynDOLOD could come prepackaged with hybrid mushrooms (don't know if that's possible or needed.) Or new mushroom rules could be added to the mesh rules index.
Just thought you might be interested in this topic.