The best interpreter of internal martial art Master Wang Xiangzai called his style YiQuan (意拳）instead of using the style name he learned from his master: XingYiQuan(形意拳). Xi means visualization and internal sensation. Xing means external form. Why he dropped the word Xing? Did he simply use a different name with no specific meaning, or did he regard form (xing) as unimportant? Below is my interpretation or "one-point-advice".
Internal martial arts deal with both form and internal sensation. The question is which is primary. This question of the primacy of form and internal sensation looks academic at first sight. Isn't it that it is all about form AND internal sensation? Take another example in tai chi. What is the primary concept in tai chi? Relaxed/open and heaviness (鬆沉) is the answer.
Master Wang is a great teacher. His primary concern was to teach and to teacher most effectively. In teaching the internal arts, Yi is of primary concern while Xing is a secondary concern. Same for Yiquan, same for tai chi. For example, when doing zhan zhuang, a student should NOT follow the form "faithfully" (such standard forms can be easily Googled nowadays for free), instead he should follow his internal feeling or Yi (in the lingo of chi kung, it is called Chi-feel 得氣感). And the primary input of a good teacher, as far as my teaching is concerned (which I believe the master shared the same), is to feel the chi of his student by chi-touching his arms/hands and adjust his internal chi according to "what is there". Since the initial conditions of each student will likely to be different, the insistence on perfect form will be counterproductive to good progress.
Master Wang said it clearly in this statement of his: 但求神意足，不求形骸似 , translated as "(you should) only seek fullness in your internal sensations and visualization, no need to seek for form perfection."
In tai chi Relaxed/open and heaviness (鬆沉) are also internal sensations.