How we do our form, how we use our techniques is also how we do fajing. There should not be any difference between the three of them otherwise what we learn in our form would not be useful to how we apply our techniques and our fajing.
In this clip I explain why we should keep proper posture when doing fajing otherwise we expose ourselves to attacks.
In addition, if we use proper posture our hands would be charged with energy. In this clip, even though I was not trying to apply fajing but the use of proper hand shape enabled some power to be transfered across.