I have my EP-3 in hands only since yesterday, so may be I'm just misunderstanding, but the AF zoom function is not behaving as I expected.
In particular it is not enough to press the zoom button once to activate the zoom of the AF area and, more important to me , the zoom setting is not recorded and after a power off I have to set it again (even though the zoom level (14x in my case) is maintained).

This is from Oly USA FAQ How can I adjust the size of the AF sampling area the camera uses?

This camera obtains autofocus by sampling a portion of the image data in the scene and searching within that area for the subject with the greatest contrast. This AF sampling area is indicated on the OLED screen by the AF frame (standard operation) or the zoom frame (when shooting using zoom frame AF).

The AF frame has fixed dimensions; however, the size of the zoom frame can be reduced by adjusting the magnification factor of the zoom frame AF function. As the magnification is increased, the size of the zoom frame decreases. Because the camera only considers the picture information within the zoom frame when it sets autofocus, the result is that the camera uses a smaller area of the scene to determine focus. This configuration makes the camera achieve autofocus with greater precision than when sampling using the AF frame.

To change the size of the AF sampling area, please do the following:

Press the Zoom button once. The zoom frame is displayed on the OLED screen. The first time this function is used, the zoom frame is configured to use a magnification factor of 7x.
Press the INFO button once. The magnification factor will be displayed in the bottom left corner of the LCD screen.
Press the Up or Down buttons on the circular keypad to select a magnification factor. The options are 5x, 7x, 10x and 14x. As the magnification factor increases, the zoom frame shrinks. Once the zoom frame reaches the desired size, press the [OK] button to register the setting. The area within the zoom frame becomes the new AF sampling area. Only the image data within the zoom frame will be considered when the camera sets autofocus.
The zoom frame can be positioned anywhere within the scene by using the arrow buttons on the keypad. When the zoom frame is displayed, pressing the zoom button will enlarge the image data contained within the zoom frame until it fills the screen. Pressing the zoom button again will end the zoom AF display, and the zoom frame will again be visible on the screen. Note that the zoom frame AF function only magnifies the image on the screen; it has no effect on the resulting captured image.

When the camera is powered down, the size of the zoom frame and its accompanying magnification factor remain registered. Therefore, if you prefer to shoot with a minimal AF sampling area, you may register a smaller zoom frame and it will be set when you next turn on the camera.