You guys often ask me how come my cake toppers don't sink even though they have such large heads :) Below you'll find some TIPS.
4. If the paste you are using is soft and dries slowly, add CMC powder (tylo powder/tylose powder) to it.
  • CMC makes the paste thicker/firmer and speeds-up the drying time. 
  • Add it shortly before forming the parts. Knead the paste well.
  • If you don't add CMC, the fondant will be soft and the cake topper will sink.
You'll find more info about CMC and hot to use it here.