The 1.2k arrisun or arrisun plus have no problem on being pointed straight down, no risk of burning nothing i'm really sure.
I've rigged a lot of times and no problem......the arrisun 5 (575) can have after long period problems of lamp because the fixture i'ts very small and hot. Just chek the color temperature after some hours. Rent some head cables more, here in italy standard rent it's the lamp, ballast, lenses, scrims, burndoors, and two for each hmi, that is about 20 meters of cable. If you can't put the ballast on the grid with a rachet strip and chain it too for safety (overhead needs safety chains for the lens, the burndoors and the fixture)
The joker bug will be the hottest because it's very very small, the arrisun and the M series have no problem of position and no problem with rain (i said rain no storm) until 6k. With the rain the real problem is the lens, only one teardrop of rain can crash the lens for thermical shock, really crash it like a bullet.After 6k arri says you cant put 12k or 18k overhead because they can burn recflector and fixture. The only fixture that can fly in the grid it's the Alpha 12/18k of 5600 lighting, It'sthe smaller and the only one.
Overall i agree that have bigger sources like bouncing muslins or ultrabounces it's better, but in the way of filtering the light maybe the silk i'ts the right way but with hmi i prefer grid cloth.