[Opinions] Re: How do you feel about not-so-obvious nicknames?
I almost always think that they need to be fairly natural shortenings of the sound of the full name, even if they're a bit childlike. If they are artificial, it seems forced, like it was the preferred name and was chosen to derive from a longer name because it was too "nicknamey." I'd rather just have a nick as a full name, than be, say, Aurelia with the "nickname" Rory, or Veronica "nicknamed" Vic.
"Ron" for Cameron seems contrived, since when I say Cameron, the ron part doesn't even sound like "Ron." It would only be because I thought Ron sounded cooler than Cam or Cammie (not that Cameron needs a nickname, IMO). And nicknames aren't about sounding cool, to me - they're just about making a longer or more formal-seeming name become shorter or more informal, for the purposes of personal, familiar address.
The only one I have on my list that I know is artificial, is Zil for Denzil. There aren't any Zil names, and I like (as a GP) the idea of a guy named Zil. Soooo... I decided I liked Denzil. And that kind of thing, is where I get my impression that such nicknames are contrived. Because if I did it, it'd be contrived.
I don't think it has to be the main stressed syllable that is used as the basis for a nickname, but it needs to be at least the first syllable (like Penny for Penelope) or a secondary stress (like Nora for Eleanor). Eleanor is EL-uh-Nohr, but I say Cameron like "CAM(uh)r'n," so Ron doesn't fly. If I pronounced it CAM-uh-Rawn, Ron might seem natural enough.
Contractions and consonant swapping work okay, especially if the stressed vowel is preserved, like Romy for Rosemary and Nell for Eleanor and Pippa for Philippa. The only nick on your PNL that I don't think is natural "enough" is Codie for Cordelia, but that depends on how you say your R. In the UK it could work, but not so well in my accent. I think a Cordelia would become Delia, Deedee, Dia, or Corie.