Hoya soidaoensis flowers are different from Hoya caudata and H. flagellata in one important way – They stay open all day and all night.  Hoya caudata and Hoya flagellata flowers close up almost entirely during the most of the day light hours.  The same is also true of another close relative – Hoya phuwuaensis; the flowers close during the day.  So from a standpoint of flowers alone, Hoya soidaoensis is the superior plant!