I would stop worrying about that. You cant pick oil ratio based on viscosity. Also be aware that two cycle oil is a mixture and once the solvent flashes inside the motor they are all much thicker.
Detergents as used in oils dont function like you think they do. They dont clean per se, rather they prevent buildup from starting in the first place.
As I told previously no two cycle oil will remove deposits. Running conditions can help as can carb tuning, but its slow process and it may never have any effect
Echo probably doesn't care about there four mix e line enough to give it a dedicated oil as the majority of their line is two stroke.