I had a supercat out on a hike couple weeks back (first time in a while, so many stoves!) and it would not blossom - then I remembered, and moved the windscreen out about an inch all the way round, off it went like a rocket. The other bit is to have a square of foil on the ground under it if it's been cold at night - the ground is a really effective heat sink.
"In the beginner's mind there are many possibilities. In the expert's mind there are few." Shunryu Suzuki