I grow both the regular Hoya engleriana and Hoya sp. aff. engleriana ‘Vietnam’ the same way, but their behavior is completely different. The regular engleriana is very difficult to grow; even when it is growing well, it can go downhill virtually over night, and be virtually dead a week later.  Hoya sp. aff. engleriana ‘Vietnam’ is a much hardier and visually appealing plant and will grow well and flower in the regular house with no artificial aids growing in my regular chunky mix.