Servus Hans,
I do not have bottom heat or mist, but have a reasonable success in striking semiripe cuttings in summer- using Hormone rooting powder and 50% each of peatmoss & Perlite and covering the pot with plastic. I also encrease my stock by pegging down branches[ with strong wire]on my old plants[ 20 or so years old & 30 -40 cm in diameter], first scaping a little of the bark away, dusting with hormone powder and mixing peatmoss and Perlite[ or sharp sand]with the soil & make sure it never dries out. After 1 year or so, you should be able to cut the rooted layer from the mother plant and pot it up.
Good Luck, Otto.