I'm Chinese, and though I'm not great at it, I do know some Cantonese(the language). Song means loose to me. For instance, you might use "song" when you say my shoe laces are too loose. Fang Song means let go, become loose. Thus, Fang Song is an action, becoming loose, Song is a state of looseness. Of course, not having any tones in the Fang, the Fang you're referring to might be another word And yes, I think openness is an important aspect as well, but I think it comes naturally if one is relaxed and practices opening the body in various ways (for example, the back during single whip)
Sincerity, knowledge
Liang Zhi Cheng