First of all, the style I practice is derived form Yang, it has some changes here and there, never practiced traditional Yang style. Nevertheless, the application I was taught for yema fen zong is basically a forward arm "break", think of Split (Lieh) but instead of using a horizontal circle, it uses a vertical one. So it's basically forward, not oblique in any way.I don't think anyone mentioned the oblique aspect of these techniques.
Basically this: [not allowed to post links, sorry, see: youtube video with ID: V9BNkuOpnWk].
The purpose of the movement in tuishou is mostly to find a line in your opponent and then just push him or transform from there, to do that you apply just a little pressure against his elbow, just enough so that his shoulder pops up, once you made him raise his shoulder you can just push him easily. Note that the arm below is basically doing Ward Off (Peng).
Now, while this application moves forward, the most common way to transition out of this position is to continue the movement of the arms forward into something similar to this appliction. [Sorry again, see Youtube video with ID: 67E3WAcW1Mo].
Hope this helps!