From Cokin makers themselves - the P holder is good for 28mm on 35mm format, the wider P holder is good for 20mm on 35mm format.
Accounting for the crop factor, the 17mm is probably still a little too wide. It might be less obvious when you try to stop down the aperture at 17mm. Objectionable vignetting can be easily corrected in post-processing. Maybe Ahbian shot the pictures at a much smaller aperture
If you do not want to trim down ur existing P holder or to purchase a slim P version or even the larger holder systems, you can try handholding the filter instead the next time.