The short story is that the plain text for the article is in Minion, so I used the end cap serifs from its uppercase ’C’.
A longer version is in http://www.typophile.com/cms/node/48851.

I don’t modify my Minion, I have a separate font for the IPA symbols (touching on Font licenses that allow private modifications?; I would consider this a highly related issue). A separate font is a bit of a hassle in everyday use, but I’m not too keen on trying to improve on Slimbach.

It has been suggested I should use open source fonts for just the IPA characters, but — as you rightly remark in your other thread — these IPA characters appear in otherwise regular phrases. Admittedly, an alternative would be to set the entire text in the same (open source) font. (Not that I have that option, realistically.)