I think if the bark of the Adenium is still not thick enough/hardened enough it may suffer from too much direct sun. But once it is, it can take all the sun and heat happily as it does here during our very long dry months. And our summer heat here is the dry, furnace type with dismal humidity too. In late fall to winter it is different, it really craves for that sun but then temps are getting cooler. Eventually, it just rests and waits for the return of better conditions, unless you really provide them the temperature it prefers at the height of winter..expensive heating cost I would imagine, but for me cheaper to let it rest.
