Sorry, my English is not very well, but I’m working on it 
Here’s the question in Chinese:
如何限制支撑仅基于打印平台，我希望支撑不会生成在模型本身的表面之上，要如何设置呢？
Generally, supports only go where you need them. There is no way to limit supports to the build plate as the slicer does not handle that, so maybe the new one will. You can adjust the support criteria or change the model, or you an edit the supports manually and delete the ones that don’t touch the plate.
Having recently played with another model of printer that has both very strong support options and also has dissolvable supports, I’m finding that the supports tend to be pretty good on the Tiertime.
Sorry, as this doesn’t directly answer your question.