Yep almost all the P4's I've seen have needed the 5th line lengthened.
either lengthen the 5th line a little bit or lengthen the z-bridle part of the 5th line by 4 inches.
per powerzones recommendations.
I have also had to shorten my mains on both my 15m and 10m P4's by 2-3 inches inorder to get them more centered on there sheeting range. before I did
this both kites would back stall when I pulled in on the bar unless I kept the trimmer at fully depowered. if you decide to shorten your mains do so
by shortening the black piece of rope between the aluminum block and the trim strap above your bar.
Regards,
Christian