TX valves are not simple (except mechanically!), as they adjust superheat. Superheat is a concept many struggle with. Here is a good article on the subject https://www.achrnews.com/articles/96890-understanding-superheat
So, in this case, what I was talking about is that the TX valve also regulates how much refrigerant can pass, and effectively slow down or speed up the flow rate in the system. The frosting on the return line is where the liquid refrigerant is getting to before reverting to gas.
If the flow rate is too fast, liquid can get back to the compressor - cant compress liqui