By necessity, the iPad camera is off-axis; the bigger the screen and the closer you are to it, the more this physical limitation becomes apparent. This effect is not limited to iPad, but similarly affects all computing platforms that employ a front-facing camera.
Unless you are looking directly at the camera, you gaze will never appear to be looking in its direction.
When comparing with a a desktop or laptop PC, the camera is most often placed at the top as opposed to the side of the screen (as is the case when using your iPad in Landscape orientation). As such, when using a PC, you gaze may appear to be below and away from the camera axis. A correctly positioned laptop will have the top-edge of the screen (and hence the camera) will be approximately at eye-level. Whilst your gaze will still be directed downwards, the off-axis effect will be minimised.
It follows that the only way that this limitation could be fully resolved is to place the camera lens dead-centre - looking through your screen. Clearly, this is not a viable proposition.
In conclusion, there is nothing that you can do - other than to place the screen slightly further away to reduce the unavoidable effect.