How do I hide my virtual objects behind real-life objects using MRTK 3?

Hello!
I have a unity app for hololens where I use MRTK 3. In my app I have an avatar (that I don’t control, I just see it move around) that moves around and a few buttons.
I would like to ask, how do I make my avatar not cross the ground or float on air? Right now it is working because I adjusted its position to my height but if someone taller than me uses the app, it will be floating.
Also, how do I make it partially invisible in order for it to behave like a real-life object? For example, if it goes near a real-life table, I would like to not see its feet because they should be hidden behind the table. In summary, how do I hide my avatar behind real-life objects using MRTK 3?