Because CT are a longfin variation and PK are short fins it's hard to get the web reduction in the short finned variety. Spawning a CT to a PK will not give you any short finned bettas in the F1. I believe that it takes a LOT of selective breeding to get CTPK and even then it doesn't prove to breed true.. I'm not 100% sure if that's correct but I believe that's what I read about the subject.
*Be smart.. Do your research!!*