1. Some turn the fist in at the end and turn it into a long-range upercut
2. Some keep the arm straight and level with the head above
3. Some lean under the arm and extend further
Here is LSW demonstrating it: notice the straight arm
Now here is a video of Tony Kam, a well-known lama pai sifu:
[youtube]http://www.youtube.com/watch?v=a6Kx4iXZbW8[/youtube]
There are many rising pao chui's in this vid. But notice in almost all of them the lama practitionner leans under his strike, tucking his head in. This is made possible in large part due to their sweeping footwork structure, but I feel this provides for more extension, more power, and is a better position defensively as it covers the head from the front (at the cost of exposing more ribs). Also, by leaning under the head is no longer "in the way" and this allows for a longer arc, and allows you to use more of your shoulders and back for power.
I understand the interpretation shown by LSW is less "committed" (perhaps this is another example of lau principle in our flavor), but I have tried it both ways and I am really liking the lama version. Now if supposedly this sequence is from lama pai, then perhaps it might be worth keeping in mind some other ways of performing it? especially since arguably the lama-version is "the source".